Tricky when it someone you not had issue with before and also unusual circumstance. It not like he's saying he don't have fees just that he's physically stopped from sending by bank issue. That doesn't help you pay your bills though.
I think it harsh to term although you can because it might take time to fill place and it not as if parent refusing to pay or over spend. Once account is unfrozen, it doesn't seem like you'll have problem being paid, it just matter of how to address delay.
Try e-mail him. Explain that although you empathise with the situation he in, that now having affect on your finances and your ability to pay own bills.
Ask him for clear answer about what bank and he are doing to unlock his account, when will it be, is bank providing him buffer finances until his own money accessible, how long will it be? It good he already know about late fees but terming just create other issue when this been good client and no reason to expect repeat of this rare situation. Just need information about when you be paid and go from there.