I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
The security deposit can only be kept by the landlord for two reasons: to cover unpaid rent or to fix damages you caused. They can't charge you to replace the blinds if you didn't break them. They also couldn't charge you for replacing the blinds if they weren't new when you moved in, because that's something that loses value over time.
Washington law only gives the landlord 21 days to send you a written, itemized list of damages. If they waited more than a month before mailing it, they have forfeited the deposit and must pay you three times that, plus attorney's fees. RCW 59.18.280. In that case, if you send the landlord a letter demanding a refund along with a copy of the statute, they could refund your money. It helps to include a deadline in the letter.
Alternatively, you can go ahead and file a suit in Small Claims Court for the money the landlord kept. Here is more information, with forms.
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