cancellation of contract

My mtn contract has expired on 07/04/2015 ,I have since then been trying to cancel the contract but had no success in all my attempts. After wasting my time holding on for (25 -35min)every timer for an operater to assist me and reference numbers ,I've had no sucses in canceling my contract. Mtn call center persenel only logs the call and tells you that it will be done in about 2-5 working days but after 20 working days it has still not been canceled and now they are holding me responsible for a another months installment and suspended my calls for non payment !!! WHAT DO THEY MEAN IF THEY SAY PLEAS HOLD THE LINE YOUR CALL IS IMPORTANT TO US ???WHAT DO CUSTOMER MEAN TO MTN IF THIS IS THE KIND OF SERVICE YOU GET FROM THEM AFTER 15 YEARS OF LOYALTY !!!!