Bad service

In May 21 i took an upgrade on my contract with mtn at cape town international airport, because i was unhappy with the terms of an upgrade i returned the phone within 8 days without using the phone and requested for them to cancel the contract but the manager informed me it was too late and i had to pay the cancellation fee. I queried this with othe mtn outlet and head office, and i was informed that as long as i brought the phone back within 20 days there shouldn't be any problem but the airport manager insist that he will not cancell the upgrade, furthermore they still deducted instalment. The phone is still with them and not with me. I have sent countless emails to the area manager of cpt international airport to no response. I would kindly appreciate your help with regard this. Nothemba Ngaju