Yeah they’re playing on your good faith and hoping you’ll just go, “Oh yeah, ok, makes sense”.
Same trick used by bill collectors who threaten you. They hope you believe them when they lie to you.
I hate law, lawyers, etc but maybe you’ll get lucky and a single, firm letter explaining the law and that they’d better drop it, give you your security deposit back, no harm, no foul.
Depends how annoyed you are and how willing you are to work with law/lawyers etc. I hate the whole thing, so I go small to big and hope smaller measures work. But if you’re a blast-them-with-all-guns, you can go that route. Depends on how you feel.