Cancelled contract a few months ago, and I am still being invoiced

Firstly, I apologize for not writing this in Dutch as my Dutch skills are not yet advanced enough.

I moved to a new address on the 1st of June and requested an address transfer, but I soon requested a cancellation of my contract with KPN as the home infrastructure does not allow me to connect a KPN modem. I called your tech support services, and I was assured that other than 1 single payment that I still had to do for the following month, that the service would be cancelled. However, I am still being billed by KPN now, a few months later.

Please cancel the contract. I cannot use KPN at my current address and I should not be paying for a service I cannot (and no longer want to) receive.