You had to go to this dealership because YOU are a sub-prime borrower. YOU made yourself a sub-prime borrower by not paying YOUR BILLS on time. Now that we have established that FACT, lets look at a few other points you make...
1. You agreed to make every payment on time, every time...on or before the due date, not one or two days late. You get all upset because they call you. Of course they will!
2. There is no grace period and that is exactly what you agreed to when you signed the contract. Did you read it?
3. Because you made yourself a sub-prime borrower your interest rate is higher than a person with good credit. When you make the payments, interest is paid at the beginning of the contract period. Because the interest is so high (which you agreed to), the balance will go down slower. Late fees which you have apparently have been racking up are a factor too. This is a fact of life for any car loan.
4. I know you haven't a clue about finance, (maybe its time to start learning), but taking the car back isn't going to hurt them a bit. It will be a voluntary reposession and carry all the effects of an involuntary repo. Who's it going to hurt? Guess who?
You have a history of bad credit. In the past, you haven't paid your bills on time. It seems like this is habitual with you. Why not turn over a "new leaf" and learn the required discipline to do the responsible thing. In time, your credit will improve and you won't be sub-prime anymore.