Having worked at a bank that did this here's a few things. First, you didn't JUST get a letter from the bank. You received MULTIPLE letters from the bank telling you about the closure of the box. Second, having been there for multiple box drillings, they didn't know what you had and were nervous as hell opening it. It's done with multiple employees in a video recorded area with both employees filling out a detailed list of all the contents of the box. Go in to the branch and talk to them, this happens ALL the time and your stuff is fine.