Telkom overbilling

I have a mobile Wi-Fi unlimited with Telkom and I have been paying R449.00 . All of a sudden I got a billing in September that I must pay 679.00. It was debited from my account I queried that in September they said it’s a problem on their side they will refund me and that did not happen. Come October same thing happened and now it was more by R80 again I phoned them and promised to fix the problem but still nothing has been done. Now for November I received another invoice with more amount to pay this time it’s about R759.00. They are still promising to fix. How long will they keep on overcharging with something I don’t know and keep promising to fix it like does Telkom think we work to pay for their mistakes , does it make sense. This is really absurd I’m so pieced with their service