My service experience

Cancelled my account in December 2024, I paid the cancellation fee. Since then they have been trying to charge me and they said if I don’t return the router on time I would owe them R600. I tried calling and emailing to check where I could return the router but received no response. Now I’m being billed R1000. The only thing they had to say was that my account has been transferred to credit bureaus and that they tried contacting me July 2024…mind you July 2024 I hadn’t even cancelled the account!