Was Fired And Boss Is Requesting An Item Back That I Was Given As A Gift, When I Met The Terms To Keep It (washington State)

EDIT: some clarification, I wanted a written notice of termination both for my personal records as well as for ease of getting unemployment, it isn’t needed for anything or required in my state. Plus he’s acknowledged his letting me go by refusing me the written letter so that really fulfills the purpose I needed it for anyways. Didn’t want him saying he hadn’t actually fired me and screwing me out of unemployment or who knows what. Thanks!

I’ll be keeping this intentionally vague to avoid being traced back to me, so please let me know if there’s more clarification needed.

I was fired from my job, and my employer requested I give back an item. This item was given to me to replicate a program one of our vendors offers, they provide two employees of a business with an item from the company to have outside or work hours to promote the vendor. My boss offered me the same out of our inventory as we already had two employees partnered with the vendor, but he wanted me to participate in the program as well.

The vendor states that once an employee has worked for the business selling the vendors items for over a year they get to keep the item, even if they leave the company. The agreement of my boss to provide this item to me was entirely verbal. He said he was doing it to match the vendor company and their policy specifically. The item has been taken out of our inventory, adjusted to me specifically, and is something I take home with me when I’m not at work. I recently just passed my one year anniversary of employment at this place as well. The item is approximately $4k.

My boss is refusing a written letter of termination until I return this.

Since this was entirely verbal communication am I sol? Would I potentially have a case as I have written proof of the vendors policy, my start date, and proof of employment for a year? Thanks!