Bad service

I have had a problem with my voicemail not being available since December 2018. I reported this for the first time in January 2019. Since then I have reported it numerous time at the call center, be means of e-mails and at the MTN shop in Boksburg. I received reference numbers every time I reported the problem. I have also received sms's each time after I reported it to inform me the problem has been resolved. Each time I responded by letting them know the problem has not been resolved. The latest one I requested the technical department to phone me to explain to them what the problem is. No response at all. This morning I contacted the call center again and requested to speak to a supervisor. I was told that the supervisor will call me. Quite right, I have not received a call. In the mean time my clients get annoyed with me for not responding to a sms notification of their call that I do not receive.