Ignore it .
See what happens.
I’ve gone through this in the past and have always ignored to first notice. Then comes a second with some vieled threats in it. Finally they start sending one after the other, each increasingly more threatening.
Sooooo, I took a big marker pen and filled out everything incorrectly. The marker ink bled through to where it was illegible.
Never heard from them again.
Doosh Feds!