Hospital billing me 4 years after service

Hello,

Texas resident here. I spent around a week in a DoD medical facility back in July 17 of 2019. I provided them with my insurance information at the time, but never received a bill of any sort via mail or any other form of communication. And as far as I can tell at this point, they never filed an insurance claim with my insurance company. Fast forward to August 17, 2023 (4 years and 1 month later to the day) and I receive a bill from the DoD for $15,693.50 (well beyond my maximum out of pocket for out of network providers, which leads me to believe they never filed a claim with insurance, correct?). The invoice date on the bill is August 17, 2023 for services rendered July 17, 2019.

At this point in time, I have a different insurance provider altogether and they certainly aren’t going to pay for the services since I wasn’t under their coverage at the time. I have reached out to my old insurance company but they don’t have a claim for services rendered on that date.

Is this legal? It seems insane that they can charge me 4 years later for services that they didn’t consider my insurance for and didn’t bill me for until now. And now that I’m not under that provider anymore, I can’t imagine they’ll be willing to pay it now (no longer have an active member ID or account or anything).

Any help is appreciated!