I have read somewhere if you have a legal lease drawn up for a year long period, that would indicate that you are not fultiming. The only other problem that you could have is producing utility bills with your name on it. If you were paying council tax , that would be good proof. On the voters roll would be good as well.If that’s you registered address and you live there I don’t see how you are fultimers.
Maybe you need to pay a small amount in rent if you don’t already.