No response on queries

Cell c handed me over when my account was already paid up, even over paid for that matter. I have been requesting the paid up letter through different emails, but none of them has ever been responded to. I had a new case number opened by a consultant, but that too has never been answered to. On top of that, I had requested a refund since March on several emails, that too has not been attended to. This is frustrating because it is badly reflecting on my credit score. One would expect such a big company to be efficient, but their service is close to none existent.