Telkom refuses to cancel an expired contract

My contract expired in April 2021 and I sent a notice to cancel the contract after it's expiry date. Even though I received a cancellation reference number from they, they continued billing me and at some I decided to reverse the payments as I had cancelled the service. Telkom handed the account to debt collectors. I sent them all the proof they needed as I also had more reference numbers from Telkom as I escalated the issue. In January I was informed by debt collector that they have finally closed the issue. Now I got another sms - notice of demand from Telkom for the same issue.