The official way to contact our support is either via email (firstname.lastname@example.org) or web: https://support.boxcryptor.com/display/DOCEN/10.+Contact+us
In our experience login problems are related to really providing the wrong password, but of course there's always the small chance of a software bug. Please double check the password or/and the process of copy&paste. If the problem persists, please include a debug log when contacting us:
1) Enable logging (Tap on the three small dots in the lower right corner of the sign in screen)
2) Try to sign in
3) The debug log will be located at "/sdcard/Android/data/com.boxcryptor2.android/boxcryptor.log"