complaint about billing

My complaint is as follows. I cancelled an LTE router contract within the cooling off period due to no signal and the router was returned. I was given written confirmation that the contract was cancelled by Cell C. I keep on having my current account debited for the contract despite numerous calls and emails to the accounts department that the contract was cancelled and that no money is due to them. I keep on being reassured that the issue is resolved yet I keep on being debited an amount of R495. will someone please finally sort this out once and for all.