I bought a car without being told it had been totaled from a car salesman?

i was never told that the car i purchased from a car lot has a total loss, i found out when i received my registration, the car lot is making me keep collision on the car as well, is this right? Is there anything i can do? My check light came on not even 30 days after purchase and they are willing to fix it, but my insurance company said i am really paying collision for nothing since its already been totaled