still paying for an expired contract with Mtn

An agreement on phone contract exhausted in FEBRUARY 2015, I called in march because money was still debted from my account by MTN. I called mtn and i was given a referance number and i was informed, my matter will be dealt with within 2 days, it never happened. Since then , i have continuously called mtn customer care lines but no consultant is available. This month i paid double the monthly instalment, i dont know why and nobody is available to explain. It was easy to join Mtn and to endorse and close an agreement with mtn, but now i feel i am being ******.