Unsure of your province, but are you with an insurance broker (not a direct writer like Co-operators)? Ask the broker or their claims people.
In Ontario, in order to assess fault under DCPD (no-fault) provisions, the third party you hit needs to confirm you were involved in the accident - and likely - that the event as transcribed by their client jibes with yours.
In this way, the person you hit is not penalized for the claim as a Collision or Comprehensive loss as they were not at fault - assuming the correspondence is NOT from your insurer.
Otherwise, if the correspondence IS from your insurer, call your broker or agent.
I would suspect if this is now months later, there may be some sort of bodily injury claim being proposed by the party you hit and the insurer is trying to backfill additional information.