RSAWeb, accounting mess!!

Terrible, TERRIBLE.I Cancelled my service, was told I would have to give and pay for a month's notice - which I duly did. Heard nothing from RSAWeb for 2 months. Sent an email checking it was indeed cancelled, received a reply from RSAWeb confirming the service was cancelled. Also received notification from Octotel confirming it was on a month to month basis and was cancelled. Then I started receiving invoices and statements saying I was overdue. I emailed and called their accounts dep to find out why I was being billed and was told someone would get back to me. Noone has called. Now they have handed my account to debt collectors and can't explain why they continue to bill me.