Voicemail doesn't work

Out of the blue, my voicemail stopped working and I have been unable to access my voicemails for months. And now suddenly, when incoming calls are diverted to my voicemail, the message is that the person has dialled the incorrect number, which is not the case!!! I have been to an MTN branch 3 times, each time the consultant has reset the settings and told me to wait for 24 hours and the voicemail service should return to normal .... nothing!! I have phoned 808 for assistance, I have been put on hold, had my call dropped or my call has not been answered. I phoned customer care and was told that my sim number would be reset within 48 hours ... still not working. I have emailed customer care about 5 times and, after getting an automatic response acknowledging my request .... nothing!! Is there anything more I should be doing?<br> No one seems to know what to do ... and I am left with a voicemail service that doesn't work and callers being told that they have dialled the wrong number.