My contract is cancelled, Stop billing me!

My contract expired in Feb and I’m still being billed. I went to the store to cancel it in January to accommodate the 30 day cancellation notice, the branch staff said that would mean I would pay my last bill in Feb but I’ve been billed ever since, I tried disputing via FNB and logged cases on their app but they continue billing me. My router hasn’t been working since end of Feb even though I asked that they convert it to prepaid. I have a confirmation of cancellation from Jan already