Voicemail not working

I have signed a new contract with MTN on the 12th. Since then my voicemail functionality has not been working - callers cannot leave voice mail. If I don't answer, instead of going to voicemail, a message says that "The number you have dialed is incorrect. please try again". I have been phoning and reporting since the 12th. I am being told that there was a general error but has been fixed, and that my number will be escalated to networks to fix. I have phoned twice today only to be told the same story the first time, but the second time I was told that the notes indicate that there is no problem on MTNs side, I must visit an iStore because the problem is on my handset! Wow! I don't even use an iPhone. So....loop started again, call was logged with a new reference number to escalate to networks. Unbelievable..