Freeview is a very good deal (worth considering depending on what you watch)
As mentioned best way to get 'a deal' is to ring up and use the thinking of leaving option. Any deal is likely to involve a new contract, so make sure you're happy with what ever they offer. If you really want to push the issue cancel outright, you're likely to get call back within a few days offering something even better (and if not you can always cancel you cancellation...). All a game i'm afraid which they don't make easy for obvious reasons.