Contract cancellation and refund

Cell c contract ended in March, they debited my account for the 25th month, and I called them last month to cancel, they said I didn't pay March premium they couldn't cancel, I said fine, they debited my account on the 26th April for march and now they debited again for April on the 28th April, I called them again today to cancel, Thabiso said to me he will cancel effective end of May I need to give them 30days notice as per terms and conditions, I told him that's nonsense my contract obliged me 24months, in any case I did call them last month.and also the two sims of that contract have been lost for over a 10 months and was given the run around when I wanted to do sim swaps, I've been paying for nothing all this time now they insist of charging me for 25th and 26th month, that is total *******. I want my money for April refunded back into my account and also Thabiso said he cancelled but only a supervisor can send me a cancellation letter another nonsense story.