My take on it is this. When you took it from the first house, I suppose that was where it all went wrong because the washing machine was part of the deal with the first house and I assume that the next people moving in would require a washing machine and they would have had to provide another one for those people as you had (albeit with permission) taken it. The new place is unfurnished, and the fact that you took the machine and had use of it has really been a bonus as they could quite easily have told you that you could not take it as it needed to stay at the old place for the new tenants. So although it might seem a bit harsh, I think they are in the right as you have signed a tenancy as 'unfurnished'. Whether by allowing you to take it they have created some sort of contract I am sure someone else will have some thoughts. Sorry but I think you will just have to buy a new one.