Unauthorized debit order

I had a 2 year phone contract with telkom and I finished paying it in May but telkom kept debiting money from my account, I called them and they canceled my contract but tellkom still keeps debiting money from account. This is really frustrating because I don't know what to do. I just received an email saying they'll attend to the query that I've made and I've never made a query with them so I don't understand what's happening.