How to merge emailAndPasswordAuth with PhoneAuth in Firebase?

I am trying to First SignIn the User using Email and Password, Then after it, I want the user's Phone Number too. So what I did I first Signed the user using his EmailAndPasswordAuthon one Activity(Custom Sign in), and after it, I Signed In the user by his Phone Number on the Next activity. But since it becomes two accounts on the same phone, and I want to merge these google and phone credentials into one account.

Then I tried to follow https://firebase.google.com/docs/auth/android/account-linking, but it is giving me the exception.

com.google.firebase.FirebaseException: User has already been linked to the given provider.

PhoneAuthActivity.java

String email = intent.getStringExtra("email");
    String password = intent.getStringExtra("pass");

    Toast.makeText(this, "Email" + email + "Password" + password, Toast.LENGTH_SHORT).show();// this is working

    emailCredential = EmailAuthProvider.getCredential(email, password);

    mPhoneNumberField = findViewById(R.id.field_phone_number);
    mVerificationField = findViewById(R.id.field_verification_code);

    mStartButton = findViewById(R.id.button_start_verification);
    mVerifyButton = findViewById(R.id.button_verify_phone);
    mResendButton = findViewById(R.id.button_resend);

    mStartButton.setOnClickListener(this);
    mVerifyButton.setOnClickListener(this);
    mResendButton.setOnClickListener(this);

    mAuth = FirebaseAuth.getInstance();
    mCallbacks = new PhoneAuthProvider.OnVerificationStateChangedCallbacks() {
        @Override
        public void onVerificationCompleted(PhoneAuthCredential credential) {
            Log.d(TAG, "onVerificationCompleted:" + credential);
            signInWithPhoneAuthCredential(credential);
        }

        @Override
        public void onVerificationFailed(FirebaseException e) {
            Log.w(TAG, "onVerificationFailed", e);
            if (e instanceof FirebaseAuthInvalidCredentialsException) {
                mPhoneNumberField.setError("Invalid phone number.");
            } else if (e instanceof FirebaseTooManyRequestsException) {
                Snackbar.make(findViewById(android.R.id.content), "Quota exceeded.",
                        Snackbar.LENGTH_SHORT).show();
            }
        }

        @Override
        public void onCodeSent(String verificationId,
                               PhoneAuthProvider.ForceResendingToken token) {
            Log.d(TAG, "onCodeSent:" + verificationId);
            mVerificationId = verificationId;
            mResendToken = token;
        }
    };
}

private void signInWithPhoneAuthCredential(PhoneAuthCredential credential) {
    mAuth.signInWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (task.isSuccessful()) {
                        Log.d(TAG, "signInWithCredential:success");
                        FirebaseUser user = task.getResult().getUser();
                        linkCredential(emailCredential);
                        startActivity(new Intent(PhoneActivity.this, MainActivity.class));
                        finish();
                    } else {
                        Log.w(TAG, "signInWithCredential:failure", task.getException());
                        if (task.getException() instanceof FirebaseAuthInvalidCredentialsException) {
                            mVerificationField.setError("Invalid code.");
                        }
                    }
                }
            });
}


private void startPhoneNumberVerification(String phoneNumber) {
    PhoneAuthProvider.getInstance().verifyPhoneNumber(
            phoneNumber,        // Phone number to verify
            60,                 // Timeout duration
            TimeUnit.SECONDS,   // Unit of timeout
            this,               // Activity (for callback binding)
            mCallbacks);        // OnVerificationStateChangedCallbacks
}

private void verifyPhoneNumberWithCode(String verificationId, String code) {
    PhoneAuthCredential credential = PhoneAuthProvider.getCredential(verificationId, code);
    signInWithPhoneAuthCredential(credential);
}

private void resendVerificationCode(String phoneNumber,
                                    PhoneAuthProvider.ForceResendingToken token) {
    PhoneAuthProvider.getInstance().verifyPhoneNumber(
            phoneNumber,        // Phone number to verify
            60,                 // Timeout duration
            TimeUnit.SECONDS,   // Unit of timeout
            this,               // Activity (for callback binding)
            mCallbacks,         // OnVerificationStateChangedCallbacks
            token);             // ForceResendingToken from callbacks
}

private boolean validatePhoneNumber() {
    String phoneNumber = mPhoneNumberField.getText().toString();
    if (TextUtils.isEmpty(phoneNumber)) {
        mPhoneNumberField.setError("Invalid phone number.");
        return false;
    }
    return true;
}

@Override
public void onStart() {
    super.onStart();
    FirebaseUser currentUser = mAuth.getCurrentUser();
    if (currentUser != null) {
    }
}

@Override
public void onClick(View view) {
    switch (view.getId()) {
        case R.id.button_start_verification:
            if (!validatePhoneNumber()) {
                return;
            }
            startPhoneNumberVerification(mPhoneNumberField.getText().toString());
            break;
        case R.id.button_verify_phone:
            String code = mVerificationField.getText().toString();
            if (TextUtils.isEmpty(code)) {
                mVerificationField.setError("Cannot be empty.");
                return;
            }

            verifyPhoneNumberWithCode(mVerificationId, code);
            break;
        case R.id.button_resend:
            resendVerificationCode(mPhoneNumberField.getText().toString(), mResendToken);
            break;
    }

}


public void linkCredential(AuthCredential credential) {
    mAuth.getCurrentUser().linkWithCredential(credential)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if (task.isSuccessful()) {
                        Log.d(TAG, "linkWithCredential:success");
                        FirebaseUser user = task.getResult().getUser();
                        Toast.makeText(PhoneActivity.this, "Merged", Toast.LENGTH_SHORT).show();

                    } else {
                        Log.w(TAG, "linkWithCredential:failure", task.getException());


                        Toast.makeText(PhoneActivity.this, "Failed to merge" + task.getException().toString(), Toast.LENGTH_SHORT).show();
                    }

                }
            });
}

As Commented down I've used my own custom phoneAuth, not using the one provied by FirebaseUI, Please Help me merging these two accounts into one.

And In firebase Console it is forming two accounts.

from How to merge emailAndPasswordAuth with PhoneAuth in Firebase?