leaving a serive provider and then rejoining

does any one if you`re allowed to leave a service provider, for example virgin media, and then rejoin to get the cheaper package deal, which are only offered to the new customers and not the existing ones.

Depends on the Ts & Cs but most have a cluase which will say something like: "not available to existing customers or those who have had an account in the past xx months" ...

You could end your contract and get your wife/husband/father/mother/cat ... to start a new account.