Subroclaims demanding 12k.

Hello all, I was in an accident last year of december 2023 that was not my fault. Staying in number 1 lane while person behind me hits me on the rear left bumper, (not paying attention on their phone) and claiming I made a unsafe lane change from the number 2 lane into his lane.
Letter:
"Our Client Geico has assigned an underinsured claim for an accident in which you were involved to our office recovery. This has occured because you were underinsured per your policy limits. Our client holds you financially responsible to cover the underinsured portion of the claim."

Now after this letter I checked my insurance (progressive) to see if the person ever got paid out for the accident.

Payout
Bodily Injury: 0
Property Damage: 0

After seeing this now i'm thinking to myself either progressive is denying liability and not paying the person out, and now the subrogatiom agency is coming for me individually. Would I need to contact a lawyer for this? Or ask my insurance what this is all about.

Thank you responses will be appreciated.

Edit: added backstory