Bad service and refund request

I saw an ad for black Friday specials and requested a call back from MTN South Africa, I received a call from an agent saying she's from MTN. I took up a contract over the phone and my sim card arrived. I was dissatisfied with how the Sim worked as the agent did not explain fully to me how it worked and was dishonest about the amount of data I was to receive monthly. So I called to cancel the contract on 6 December within the given grace period for cancelations and they have debited my account for 3 consecutive months since December, twice on days that were not my paydates, which cost me banking fees. Only when I was canceling the deal I found that I was talking to an agent from Mondo and not MTN so I have been calling both companies to complain and request for my refund with no resolution. MTN keeps redirecting me to Mondo and their retention team but I am not getting any help. They hang up the calls and don't call back or give feedback.