Distgusted by Cell C service

I've been trying to get hold of Cell C for 2 days now to cancel my contract with them because I needed a paid up letter. I eventually got hold of them today only to tell me that they can only terminate my contract next mont because I still need to make another payment for a contract that expired last year already. They deducted the same amount since the contract ended which is **************** after you paid for the device already. Their question to me was "why didn't I contact them earlier?". Well, how could I if you on the line for almost 10-15 minutes, their lines is always busy and if you go to their outlets they tell you that they can't help you and that you have to phone in. What's even more confusing is the fact that you have to sign all your papers at the outlets if you take out a contract but when you need a paid up letter you need to phone in, why can't the outlets issue you with a paid up letter. Their service just poor and they can't give you proper answers everyone is telling you a different story. I'm disgusted with their service it's an utter disgrace!