What can I do if an insurance company says I owe their client when I don't recall hitting a vehicle in a car wreck?

I recently received a letter stating that I owed money to an insurance company's client, from a wrongful accident that happened back in February. The accident occurred during bad weather (a snow storm). It also occurred on the interstate, in which a bridge was not covered in sand, and many cars lost control and wrecked almost at the same time. I don't recall hitting anyone's vehicle, but that's what the letter stated. I am helpless.