This happened to me a few years back.
The person i hit on left rear quarter did the same i pressume that happened to you.
He kept denying that it was his fault.
So with my cunning tongue, when we are on a 3 way conversation with the insurance company. I asked him, did you check your rear vision mirror? He said yes, he also lead to say that he didnt see me there. So i said, you didnt do a head check when you merged, he said he checked his passenger mirror, i then said, you didnt check your blind spot. The case manager then said that i was not at fault for his neglegence.
I hope this plays out the same way for you.