Yes. As long as it is closed, its contents are protected from fire and water. The Underwriters Laboratories (UL) has certified the 2037F to withstand temperatures of up to 1,550 degrees for half an hour. To know more details about this product you may visit here : First Alert 2037F Fire and Water File Chest Review Here you can acquire more helpful knowledge.
Although I'm sure your a legitimate owner, there is a way to open these without the combination that's non destructive, I can't describe here in the open forum, you can google the solution, or call a lock smith, they probably use the same method and if they are nice,they might tell you over the phone. Otherwise because the serial# says nothing about the legal ownership. I cannot in good faith help in this situation. Good luck.
