Can my new management, go back and reverse old charges from my apartment?

Long story short, the previous manager got fired about 3 months ago. She was a cool manager that let us off the hook with late fees. Whenever we were late, she would take it off. I got comfortable, and paying on the first wasn’t a priority, but I’ve never missed a payment.

New management come in, and a few months later, I have a $2024 charge, that I have 30 days pay. This came from them reversing all the late fees. Is this legal to do ? Even if I didn’t have 30 days, but had to pay, is it legal?

Location: tri cities, Washington