Your FC house probably hadn't had anyone actually use it for over 90 days, so the land was automatically repossessed and the house demolished. It was a function that players begged SE to implement so as to free up land for new houses, given that there are plenty of houses that were sitting unused and empty for years and plenty of players desperate to get a house of their own, and was added to the game a couple of months ago.

The furnishings from your room should be held by the Residential Caretaker in each residential area - speak to him to get your items back. Just bear in mind that some items are unrecoverable and are lost for good (the sort of items that are destroyed if you put them down once and then try to pick them up again).