Contract cancellation

I took a 36 month contract and finished paying before the contract ends ,my contract expires 2024 October and I have a credit on them owing me (R595) I asked for the contract cancellation fee and I was not responded I sent an email to their retention address which I got an auto response saying I’m going to be rep**** even now I’m waiting and I tried calling I was transferred to 4 different customer service champions who failed to help me (kept on transferring me to other agents ) wasting 20min of my airtime hoping that I give up or my airtime ends in the process hence I want to cancel my contract with MTN seems like they benefit from Blacklisting their clients I want to cancel cellphone contract with them so no one gets back to me