Annoying messages and calls from strangers

For about a week now, I have received on average 250 please call me messages from total strangers, saying they received a missed call from my number, but I do not even have airtime on this phone, ever. About 40 calls per day with the same problem. I went to the local MTN shop, they could not see any problems on my profile. Later that day I phoned the ***** number, they could not assist me either. I then phoned 135 and spoke to 3 people, Levi assured me that within 2 days someone would sms me should the problem not be resolved yet.....nothing received 3 days later. I can not use my phone, for there is constantly some total stranger trying to phone me or sending me messages or whats app messages....how can they not know how to fix this problem?