Contract Cancellation

I cancelled a contract with MTN while it was still in cooling period, They told me its cancelled and I should await for an sms , a week later I called trying to check why I havnt received an sms and was told I need to pay R356.00 I do not understand for what because I cancelled the contract the nextday it was activated and was told I will not pay anything,I tried getting hold of them on twittter too but they keep saying its been escalated to management,I have spoken to Miranda on their cancellation department and she is the one who initially cancelled the contract but the second time I called in wanting to speak with her I was assisted by Rosseta who could not explain why I had to pay.This is really annoying because they debited me as to why I do not understand. Im really angry.