Here's a thought, you might not like it, but it does work.
See if you are eligible for a "bill payer loan". If you owe less on the car than it's worth, you can borrow the entire amount of the car, (sort of refinancing). Since the amount of the loan will be far less then the original loan, the monthly payment will be lower, and you'll get away from the lender who just tightened the screws on you.
My son did it, and it worked great. He went to the insurance company (State Farm) for the loan. He owed $6000 on his car, and they gave him the entire $6K, on a 36 month loan, and his payments were $183.00, and he managed to pay off the loan in 18 months with no penalty.
Just a suggestion you might not have considered.