I've had similar problems in the past
I started a new contract with Orange then cancelled it within the 14 day money back guarantee period (Due to how rude a CSO was to me).
Anyway, they had already ported my number across and had decided to continue charging me for this period, so I had 2 months or so of line rental to pay, despite having the contract annulled under their guarantee, having no phone, no service and already having re-ported the number back to my next providor (thank you T-Mobile for being dull, but at least consistent).
In the end, after about a week of my having to make stronger and stronger phone calls, they cancelled the bills "Out of goodwill". Note that they never admitted they were at fault.
One can go off companies very easily.. I think I'll be heading to Vodagroan for a while.