There's no harm in giving them a call and letting them know your situation with Sky. See what the best deal is they can offer and take it from there. Play one against the other.
Do you have access to Virgin media in your area? If so, tell Sky that Virgin are willing to give you a better deal than you currently have with Sky and that they mentioned they were willing to give you credit on your new Virgin account to help with any early termination fees. The only thing is...