Contract cancellation nightmare

I will make use of this opportunity as my last resort. December 2018 I took out a cell phone contract over the internet. After receiving the phone I realized I was **** to about being able to change the contact number to my existing number and I was **** to about the first payment. I took the phone back to MTN East Rand Mall because that was what I was advised to do by them in order to cancel the contract. Now more than 2 years later and after various attempts at cancellation the contract is still running. Please help