I've written a couple of legal Guides on this website about taking your landlord to small claims to get your deposit back. RCW 59 18 280 provides that you are entitled to up to 2x your deposit back at the judges' discretion.
The old saw about 'we did not know your address" is because California law requires a departing tenant to give their landlord their forwarding address, but here in WA the landlord can mail to the tenant's last known address and provided that you have told the post office what your new address is, you will get your mail.
The most important document in your story is the move in walk through report, and the subsequent move out walk through report. Read the three statutes about deposits carefully, and see where your facts fall.
There isn't a lot of caselaw on this because it mostly gets resolved in Small Claims. Your local law library (at the courthouse) will have dark green volumes called "West's RCWA" The "A" stands for annotated. Look up RCW 59 18 260, and RCW 59 18 280 and see if you can find a case where the facts are similar.
You might want to look for a local consumer protection attorney who *may* be willing to work with you regarding payment.
Hope this helps. Elizabeth Powell