Billing for expired contract

I had a contract account with MTN which ended on 22 March 2015, so my debit order used to go through 1st of each month.on the 1st of April i was charged R379 for an contract that ended 22 March , so i called in their customer care number and after holding for close to an hour the consultant gave me a reference number and assured me that i would'nt be charged again , the reference number was *** , but to my surprise this month i was charged again.I want my money back for the two months , because to my knowlegde i paid up the 24mnths that i had signed for and even so speaking i have been holding the 808 line for the past 45 mins.