Mondo MTN contract

Mondo rep**** to my complaint saying they can't reach me and I also got an email from them stating that they have sent MTN an email to do the cancellation. When I called MTN cancellation department to confirm if they got the email, they said they didn't receive it and told me because the sim was activated by Mondo they should be the one to cancel it, then the MTN consultant transfered me to them and what they did was to transfer me back to MTN, so when I called MTN again they told me they can only cancel the contract if I pay an amount R500. And if I pay that amount Mondo will not refund me the amount that was debited from my account. Please advice what I should do to be assisted because this thing has been dragging for far too long and it's tough out here with this pandemic. Paying for something you never recieved and nor use. What exactly am I been billed for when am not even using the simcard. What is your system say? Or is this how you **** people. Cancel the contract with emmidiate effect and give me the money you debited from my acc, because I never used your service. Today I am in arrears because you. My services with mtn will cancelled because am unable to pay them, all this is ba cause of you