unhelpful.unfriendly consultants ,customer service,

On the 24 November 2017 I took a contract phone from telkom at carnival mall store. I then returned the device unopened on the 28 November 2017. I was given a cancellation letter and was told it has been sent. To my surprise come month end its still active so am told it takes 21 working days to cancel a contract. Funny enough today I receive my statement its still on my account and am being billed for it. I call the store all morning and no one answer their landline. When I call the call centre am told that if I keep on rejecting the debt order it will have a bad credit reflecton on my profile. How do I know this time my money will be returned to me .? Poor customer service.