Non functional voicemail

We have contacted MTN call centre numerous times as we keep being referred to the call centre by the Parkview en Menlyn Retail park Branches which was visited as they cannot sort the problem themselves. I am a sales person and business owner and have a dual simcard for my cellphone and tablet of which my voice mailbox cannot be accessed although my customers can leave a voice mail. Till today a year and one month since inception of my contract this problem has to be resolved. Every time we call the problem gets logged and promises that the problem logged will be resolved within 24 to 48 hours. We then call again as the problem persists and are then told to reboot the devices which has been done at least 3 time during the last final attempt to resolve the problem. When I phone 100 to contact my mailbox I get a message that tells me the number does not exist!! Sorry MTN but your logging and problem solving system is utterly useless. After 17 years of loyal support this was the the final straw and I will be moving our 4 contracts to somebody who at least try to care!