Biggest ****mers MTN

I took a contract with MTN I was not happy with the product I immediately returned the product before 7 days. I called and gave them the Reference number as evidence that the phone was returned within 7days. On the 20th of August MTN took the amount of R733 for the contract I canceled. I called multiple times with no assistance.Now I received a statement from MTN claiming I must pay R15000 for cancelation. MTN **** people