Really getting shaft from insurance, PLEASE help/advise!

First off, hello the community out there. I'm hoping to get some answers here in a very, very dire situation for our family. I will try not to make this TLDR, but I really need some advice on what to do.

First, a bit of financial background:
Married, just had a baby so bought a house (90% of our savings). A year later Repaired and central air unit ($300). Next day, water heater blew ($900). Next day, car accident (47k miles, consistent oil changes, treated it like gold). Brought it to repair shop ($500) deductible. ($100) rental fee. We had to borrow the $900, $500 and $100 from family. This all happened literally in the course of days.

Were' now flat broke at this point.

I get the car back and the engine is very loud. I figure, "Oh well, it'll never be the same after an accident". Next day, it's louder and it stalls going around a corner. Next day it's very loud and stalls three times. I bring it back to the shop and they say, "Looks like you need an oil change". I was flabbergasted.I told him to take a look at it, get the insurance adjuster down there and see what's going on. Basically he just punched in some codes and said that "Engine rapping can be caused by bad oil". I said, that's a mighty big coincidence because 9 days before the accident I got an oil change, faxed them and my insurance the receipt. Also swore at me "Are you the F***ING professional" and "That's what you expect from a "HI-Yaa-ndai". Now, I'm the most mild mannered guy so we he got all confrontational I hung up and called my insurance, thinking they wouldn't believe what's happening and help me or advocate for me in some way.

Few days later I get a call from the adjuster saying they can't prove it's related to the accident. I couldn't believe it. He said that when I brought it back to the shop, I was told it was un-driveable. Yes, so I went and got a rental car and dropped it back off the shop the very same day, 2 hours later. Come to find out the guy at repair shop tells adjuster I drove it away and drove it all weekend. BIG LIE.

So, I got the adjuster after much arguing to pay for the tow to the Hyundai dealership and for the diagnostic.

Are they going to simply punch in a symptom and see what code pops up? What recourse do I have if they continue to deny this is related to the accident? There is no financial way we can absorb this hit right now. $100 may as well be $1,000,000 for us now.

So right now, the car is sitting at the dealership waiting for Tuesday to get here. And I'm sitting here petrified.

How does one fight this? What recourse is there for someone like myself? Any? Obviously once this is all said and done we are dropping our insurance company and contacting the BBB about the repair shop.

But what about my car? What can I do? Who is my advocate right now?