Cancelation nightmare

Absolute nightmare to cancel my data contract. I've called multiple times and spent hours on the phone to cancel. I initially called on 8 July to cancel and was told I need to pay R600 cancelation fee for a data contract (without a device) which I had originally taken out on a month to month basis and not a 24 month contract. I raised the concern and was told I will get a response in 7 business days. When I called back after this period lapsed to find out what was happening I was told the system was offline and I couldn't be helped. It's now the end of the month and MTN has sent me another month's invoice for August and my issue still has not been resolved...