Cell C does it again!

Cell C deserves 0 stars actually. Just in the past year, they have *****ed up our billing twice and now suddenly they have found an invoice that is 10 years old and want us to pay for it. I don't know what they do there but it sure as hell isn't good accounting. First problem they lose one of our payments, it first appeared on our account and then a few months later it was outstanding. How they *****ed that up only they will know, This was November, after months and months of sending proof of payments they have only NOW fixed it. Then suddenly we have 2 months invoices that were never sent to us, for a number that has been on our account for years! Suddenly for 2 months it was moved to a new account and the invoices were never sent to us. We go back check our account and make the payment, settled. Now they come up with a 10 year old bill that I cannot go back and check if I ever received it never mind check if I paid it. Is this even legal? I have no words for this company, this is beyond ridiculous!