Contact Expired but Mtn refuses to cancel contract

I came into the store in the last week of May to arrange for contract to be cancelled as contract expires on 3 June 2015. Charina assisted me at North Cape Mall Mtn branch and promised to have contract cancelled but I would retain the number. She also told me Mtn is on strike but will give info through. To my utter dismay, contract was not cancelled and I received an sms to say I must pay R199 for arrears! The Mtn strike is not my problem as they failed to cancel contract as per my request. It is me request that this contract be cancelled with immediate effect and all monies written off as I do not owe Mtn any monies. Its not my fault if Mtn staff are striking because I'm a paying client.