If you didn't have health insurance through the Marketplace, just reply to them with a statement to that effect. Print something about your coverage- an insurance card copy, a paystub showing your payments through work...
Or call the number on your notice and ask, "Why are you sending this to me?'
The notice is likely automated, so find out if somehow there's a 1095-A "out there" with your SSN on it (or your dependents). Ask the IRS if you just cannot figure out why you have this.
It could also just be a mistake.
Mistakes do happen.
Either way, it's resolvable and you just have to get the ball rolling with the IRS to take care of it.
