You would need $2,500 just to get a case going. Expect to pay $25 - 50k to go through the discovery process to get what you seek. If it is true that Chase does not have the note, then you may want to file for bankruptcy to have the note discharged, which should clear title to the property in your name.
I would call the Northwest Justice Project through the Washington State Bar Association. Their services are free. They can help.
For example, have you checked your county's land records. It is unlikely that Chase recorded their interest after getting the trust deed from WaMu. MERS may be able to fix this, but it is an open question for the court of appeals to decide (add an extra $30k to your expected attorney's fees). Also, the Project may know of a financial expert that can help you track down the note for less than what it would cost for an attorney to do so.
I agree with the previous answer.
You will need to sue in superior court to stall the trustee's sale and convert the action into a judicial forclosure to demand the note and air your complaints. This action is not an inexpensive process and you may well be better off saving your money because in the end you don't really have a right to a refi, the mediation process is cumbersome and you can demand it when they file the foreclosure under RCW 61.24.163
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