I’d stop paying child support. If you want to pay for college or help, that’s up to you. If what you describe is true, that she won’t contact you, then I wouldn’t pay. Offer her the money if she’d like to have a relationship with you as a father, but not as a rich donor who just wants to send her money. This can be explained in a letter to HER, not to her mother. Child support is set up in a certain way by law because that’s what the state thinks is fair. Different states have different cutoff ages (18, grad from high school, 21, married, join military, etc). Sometimes the amount paid reflects that. You might have paid a little more because your state knew the obligation was for 18 years and not 21, wouldn’t include college. It’s hard to say if what you paid was fair in Ohio but not in Georgia, or California, or NY. The law here was 18. My BIL paid his required amount for 15 years, and then helped his son pay for college basically the same amount as child support, but when son stopped going to college and moved back to his mother’s, BIL stopped paying. He continued to have a relationship, continued to send birthday money or take him out (son lives about 4 hours away) when in that town, etc., but the ex-wife was out of it. She always made more money than BIL and always acted like she deserved more - more time, more holidays, more money, more insurance, etc. She was an unhappy person.
As for the car, was it a gift for graduation, a birthday, all that? Do you make payments on a very expensive car? Who pays the insurance? If it was a gift, then it was a gift. If it was for her to use but you own it, then you could take it back since her high school days are over.
My parents weren’t divorced, but I didn’t get guaranteed money every month when I was in college. I earned as much as I could, my father sometimes sent me $100 for rent (but only if I begged). I never had a car in college and when I graduated I did get one - and the payment book that came with is! (he paid first payment as a gift, the rest was on me). And I appreciated it. He spent a lot of money on himself and on the kids living with him (I have 3 younger brothers) but the 3 older kids (me, brother, sister) were in college, out of sight, out of mind. And off the payroll.
My own kids (I’m a single mother with no other parent paying anything) did not have cars in college, did not get guaranteed money from me, were offered to live for free at home but chose to pay rent and go to colleges far away. Sometimes they like me, sometimes they don’t, but they never thought I was unfair or withholding money they were ENTITLED to (they knew they weren’t entitled and that I was doing my best). Now they are independent, even though one just started grad school; grad school is ALL on her (luckily, it’s fully funded but she works to pay the rent and support her coffee habit).
I have a friend whose husband died when her kids were quite young. She received social security for them and she KNEW it was going to end when they were 18/grad from hs. She planned for it! Your daughter’s mother knew the child support was going to end. She should have planned.