So disappointed by Telkom

I regret the day I agreed to a telkom contract phone and have no idea how I can get out of it without affecting my credit score. THE amount that was agreed on is R149 on a capped option but it's been 4long months of being debited over R300 each month. I have contacted them just to double check if I'm on an open contract and the call center agents confirmed that it's a top up (which I normally buy prepaid for). Someone tell me how do I get my money back and stop them from *****ing it from my account?