If your verification code is not working, there are generally two reasons: (1) the QR-code might have been scanned more than once or (2) the time on your phone and the other device are not synchronized.
(1) In the first case, please delete and reinstall the authentication app. Then, scan the QR-code again. If you need to reset your account, please contact our team at firstname.lastname@example.org.
(2) In the second case, please go to the "Date and Time" settings of your mobile phone and make sure the option to get time data from the network is selected.