Unable to cancel

I cancelled my line end of August, over the 30days notice. During this period I phoned many times to confirm that my line will be cancelled and kept on being told that yes it will be and that I would receive the cancellation email and reference shortly. But I never did. I received my invoice for October a few days ago and phoned again to make sure that my line will indeed be cancelled and again they said yes it would be and that I should receive an email the next day saying it's cancelled which I never did and now, low and behold, the 1st of October has come and my new ISP is unable to take over the line because Supersonic still hasn't released it. I followed the correct procedures and my account is fully up to date. This is unacceptable for a service that claims to be month to month.