Cause 3 of 4: You're trying to check your voicemail from another phone than your own

The default voicemail number can only be used if you're calling form your own phone.

Solution: 1) Call 021 700 700

2) You're asked to key in your "mailbox number".
This is your phone number, leaving out the first 0 followed by #) (e.g. 21 987 654 #)

3) Key in your 4-digit PIN and key in #

4) You're now in the main menu. Follow the verbal instructions to listen to your voice messages.