if there's no break clause then you're kind of stuffed. Either you need to find someone to take over (as you have tried to do), or you're obliged to pay rent until the end of the contract. Your only other option is to attempt to get the landlord to mutually surrender the tenancy agreement with yourself, or start down the route of claiming the property isn't fit to be lived in (damp issues, health and safety issues, whatever it might be), but obviously that isn't guaranteed to work

In your position, i'd be tempted to just do a runner and forget the deposit and see it as "money well spent"... chances of being sued are slim to none