Not so Supersonic

I cancelled Supersonic services 10 June 2022. Router was returned and cancellation confirmed. Fast forward to 2024 I get a call from debt collectors called VVM saying I owe Supersonic over R 1000. I explained that I cancelled my services with them and weeks later still getting calls. I have also sent e-mails with proof of cancelation to ***, ***, ***, *** and still no response.

If Supersonic service is on an a month to month basis with no contract, how do I owe them for services terminated in 2022?

I probably won't get any response from Supersonic because they have been atrocious. I regret ever using them!