Cancelled account but still getting billed

I sent in cancellation form on 16/11/2016. Later that week I get a call from the agent saying that my account would be cancelled by the 16th of December, once my access adsl was cancelled (30/11/2015). Then in January I received a bill so I phoned to see what had happened and was told that they were waiting for access adsl to be cancelled (have not received a bill since I cancelled it and phoned and confirmed with axxess). Now it's March and I've received another bill, tried to phone and sort it out but got told that they have no proof of cancellation but at the same time acknowledge they received the escalation in January which acknowledged that they received the cancellation. I don't understand why the account has not been cancelled yet.