As the message you quote say – we do not delete accounts on request. You must delete it yourself. This is for your security.
Sign in to your account and delete it at https://account.axcrypt.net/Home/Login .
If you do not know the password, issue a password reset at https://account.axcrypt.net/Home/PasswordReset and then sign in and delete it.
If this does not work, please send a screen shot of the error message describing your problem.