mechanic's car lien on a car already released to me

Hello all, (california)
I was in an accident about 4 months ago and it wasn’t my fault. I took the car to the body shop to get it fixed (damage under $2k) and the body shop told me that they will deal with my insurance directly and that I didn’t have to pay them anything. While my car was being fixed my insurance for some reason sent me the 1000 check (which is my deductible). Once the car was fixed, I picked it up, signed off at the body shop, on the paper work it did not indicate that I owe them anything so i signed off and drove off.

Here is the funny part, now 4 months later the body shop is calling me and telling me that I owe them 1000 dollars. I asked them to get me some kind of a written notice from the insurance so I have some kind of a proof that I paid them but they keep calling and threatening with a mechanic's lien on my car (which is in my position).

My question is, can they place a mechanic's lien on a car that I and they already signed off on and that I poses? This is in California.
Thanks in advance,
garo.