First, if you are represented by counsel, you should check with them. Second, with the stated intention of surrendering the vehicle, you have 30 days after your 341 to do that or the stay is automatically lifted. Sounds like they may have taken it around that time.
My response is general information not intended as legal advice or to create an attorney-client relationship. Seek advice from a qualified attorney to see how the law fits your specific facts. I am licensed to practice law in Washington and Oregon.
You definitely need to speak to your lawyer about this right away. I agree with my colleague -- BECU may be within their rights to do what they did BUT, the property in the car, as well as the tag and other similar items, remain property of the bankruptcy estate. What this means is that they may have technically violated the stay, but I suspect that giving them a call will be all that is required to reacquire your personal property.
Good luck to you!