Pathetic service and useless fibre

Pathetic account department and useless fibre. I subscribe with supersonic and couldn't get coverage, I called them and unsubscribed since it was no use to me. They then send me a bill of R3k when i asked what was that for they said because the router is still with me. I shipped the router back to them after them failing to pick it up. Now i received an sms that my account has been handed over. What am i owing them for I don't. Im struggling to get through to them