Telkom not cancelling service

I cancelled my FTTH uncapped internet contract with Telkom in October 2019. In November I moved to a new service provider and considered the cancellation to have been completed.

Much to my horror Telkom continued to charge me and handed me over to lawyers for outstanding debt collection. So then I tried to cancel my service online, only to see that I can not cancel a suspended service.

How hard can this be?