Telkom failing to cancel my contract and debiting my account for a device hat I dont have

Telkom is a ****, they are not a good company to trust. Last year around November they called me and advertised their cellphone device which I fell for their trap. They deliverd the device and only to find out that I ws not happy about. I returned it back the following day and gave the the tracking number. They did not tell me if they received it up until I called them then that's when they told me that they got it. I asked them to cancel the contract, they said I must not worry it's gonna take three to five working days. The following month I revived an invoice or bill that I have to pay, I was really shocked that I called them I told them to cancel but they did not help only telling me that if they cancel the contract I will be charged. They said they are taking the matter further but up until today I've been disputing every debit and calling them but they are not helping, now that the money is too much they are telling me that they will blacklist me if I dont pay it. If they were a transparent company they should have called the first time I disputed and ask incase my case was not attended. So now I have to be blacklisted for something that I dont even have. It's so bad coz they making it so hard to trust any company and in that way I am taking this matter further because I can't be ****med like this. This is unfair and I will never ever trust anything from Telkom, ever. I thought it was a transparent company but I was wrong.