Contract cancellation

I used to have a contract with Telkom. On the 22 May I called telkom and told them when my contract expires I won’t renew it and Philani Ndlovu sent me a cancellation form I filled the form ane sent it on the 25 May my contract was expiring in June. In July Telkom deducted money from my account I called and asked what going I was told to resend the form and it I’ve done so I’ve cc Nozipho Kubheka but still Telkom was debating my bank account. I then asked the back to reverse the transactions. Telkom now is telling me I’m owing them R700 and I’ve been back listed WHY ?