When the recovery code does not work, it is probable that you try to use the wrong recovery code.

Zivver recovery codes have a relation to specific passwords, not to user accounts. If you request a recovery code after a password change, the recovery code work for messages that you sent or received after the password change. To restore access to your old messages, you need the recovery code that corresponds to your old password. You received this recovery code on the date that you created your account, or on the date you created your password. Zivver tells you the date and time that you received the recovery code.

Do the instructions on how to restore your messages precisely.