Worst customer service ever

I keep getting calls from Vodacom’s automated system, saying my account is in arrears, when in fact it is not. At one stage I even paid my account in advance and still got the calls. I have spoken to 5 managers so far and escalated it numerous times. The story always stays the same and nothing gets fixed. It’s been carrying on for about 8 months. Managers have promised call backs and none returned the calls. Is there anyone higher up I can speak to to sort it out? After getting the call once again this afternoon, which I followed up with another half an hour call with a manager, I received the call again at 20:37 tonight. I have even blocked some of the numbers which was a consultant’s advice. It’s the worst customer service I have ever seen