Cancelled my land line months ago, still being billed

Hi, I've cancelled my land line in July, and sent all the requested documents to the servcancel email address they said I should send it to. Didn't receive any feedback, so I phoned them and then also sent the paperwork to the person I spoke to over the phone. Still nothing. I keep getting billed for a line that I don't have since July 2017.

I've send all the documents to the servcancellation email address for the 5th time today, but I don't think that will make a difference.

How on earth can it be so difficult to cancel a line?