Situations like those expressed above can result in all sorts of problems, such as being chased by unexpected Debt Collection agencies at a later date, having to pay more than you should or making you feel as if you can't leave your ISP.
In situations like this it's best to follow the 'Official ISP Complaint Handlers and Procedures' procedure and if for some reason that doesn't work then check our 'Unofficial ISP Complaint Handlers and Legal Counsel' page for details on using the Small Claims Court or Citizens Advice Bureau to fight your case (don't be afraid of them, they're setup to help you). Please also check out our Helpful ISP Complaint Tips page for additional advice.
As a side note it's worth remembering that Ofcom's harmonised migration rules mean that in most situations you can swap ISP without needing to even contact your existing provider, which is done simply by requesting to switch via your new ISP choice. The rest of the process will be handled automatically.