Cell C cannot resolve their own query

Cell C has got to be one of the worst company's to ever exist. Every month we pay them and everything is fine, then out of the blue, 5 months after payment was made all of a sudden we didn't pay according to them. Suddenly we have an outstanding amount on our statement and for the past 8 months after numerous attempts at trying to resolve this query this payment amount is still sitting on their statement as outstanding. We have sent them proof of payment multiple times, we have spoken to multiple people over the last 8 months and still they can't get this resolved. Escalation after escalation and still nothing has been resolved. I don't even know how this is even possible. Shocking to say the least. This review will probably go no where....