Bought a car and the guy I got it from will not give me a bill of sale

Location: Utah. So I just turned 18 in June. And last week I went on Facebook marketplace and I went to look at a 2008 Nissan Altima, with some transmission issues but other than that it’s fine. I went with my girlfriend and a friend (I should’ve brought a parent or someone who could help me more) and my friend wanted to test drive it after I did so that he can see if there was any issues. He test drove it and someone backed into us. Very little damage to either car, me and the other guy shook on it to just walk away. We drove back and talked to the owner of the car and told him what happened (I was already planning on buying the car so I just decided to buy it. The car was $1000 but I only had $800 cause I was waiting on my paycheck 2 days later. I was just gonna wait to buy it until I had all the money but since we got in a minor accident I asked the guy if I could just pay him $800 now then $200 when I get it. He agreed and I gave him the $800 and he gave me the keys and the title and said he’d give me the bill of sale when I get him the rest of the money, makes sense, no problem. A couple days later I meet up with him to give him the money, I give him the rest and he said he didn’t have the bill of sale on hand because he was just going around town. He said he’d drop it off to me later that day. He didn’t, fast forward to the next day. I asked him about it, he didn’t give it to me. I then showed the title to my stepdad and he pointed out that the guy I bought it from doesn’t have his name on the title and the last owner on the title was a random automotive shop called “beehive motors LLC.” I talked to my dad about the situation and he tried calling this shop and they didn’t exist, or if they did it was under a different name. So we talked to the guy I bought the car from and said we need a bill of sale or I can’t get it registered, but we also needed one from the previous owner to him, then one to me. We’ve been trying to get it for a week now and it seems like he just isn’t doing anything, he claims he’s trying to get ahold of the person that originally owned the car, for a bill of sale which he had before but said he’d lost when moving houses. I thought about it and figured that a bill of sale from the original owner to him wouldn’t work cause the original owner wasn’t the last owner on the title, but I’m not sure about that. But overall the guy just won’t give us the bill of sale and it’s really frustrating because I can’t register the car without it and I need this car for work. I just don’t know what to do at this point. Very long read, my apologies