I am pretty sure that in the eyes of the law, by moving house it is you that has broken the terms of the contract, which i am guessing (without setting eyes on the agreement itself) is to supply you with the services AT THAT ADDRESS? I suggest you check the agreement for this detail. If so you are on weak grounds in legal terms, but should consider negotiating a suitable compromise with them - ie taking the nearest available package if they will waive the fees?? This is obviously up Virgin at the end of the day, but they should really aim to work with and keep a customer rather than get a fee and loose one? Good luck.
Mark