Faaaaaalse. A) He has no legal ground to stand on, he trespassed/signed a new tenant when you still had legal residency, and billed you for cleaning before you had a chance to clean. B) He won’t want to fight it, he knows he will lose C) small claims doesn’t have attorneys, so it wont cost you anything, D) There are lots of laws protecting against predatory landlords, E) He probably gouges other people all the time and pushes them around, so you‘re making a stand on everyone’s behalf, F) he sounds like a total douche.
So, Win-Win-Win-Win-Win-Win by my count! Damages should include pain and suffering, plus punitive damages to discourage him from screwing the next few guys