Poor service

I had contracts with Cell C, paid them religiously and then could not be assisted with upgrades anymore. I cancelled the contracts at the end of the full term, and did not receive my last statement or any calls or SMS advising that there was a last payment due, as the contract was cancelled in advance. Eventually I receive calls from a collection agency which does not even know what this going on on the account. I received a statement eventually from Cell C, which I settled directly to them, as they had no contact with me and I won't deal with a 3rd party that the debt was sold to without them even trying to reach me. Now they don't supply me with a paid letter so i can get the uncalled debt collectors to stop pestering me, as they are not liasing with their client.