1st of all, I hate this word"跪謝".

2ndly, bit more detail needed to answer your question.

the way I see it, you accepted a new tenant with new lease, and you agreed to release the previous tenant from old lease, you are at fault.

each state is different, but most state demands landlord must settle any deposits in a timely manner, remember security deposits are NOT your money.

did the previous tenant providing you a forwarding address? if not, you can argue no forwarding address was provide