Heres your answer.
A 12 month contract doesn't mean you can cancel ANY time after the first twelve months, It means you technically have to give 12 months notice for leaving before you plan to.
Which is plain nasty.
AOL are about the best for service switch surprisingly, they offer for you to opt out at a minimum of 4 months notice, and whilst you still pay for those 4 months, you can still use the service right up till the end of that 4 month period.
So, if you keep in mind the contract, you can just order a new service a few days before the contract ends, and hey presto, you should have no trouble.
Plus, you didn't state that you were having any technical issues, just a dislike of tiscali (who doesn't have), so if you need to switch, id try that.
Also talk to someone who isn't a total f***wit, try to get them to knock the cancellation period to a month or two, never hurts to try.
Hope this helped