If you are behind 1300 and you offer them 1500 to get your car back and continue making payments can they refuse?

READ your contract. It likely has "right to accelerate balance due" clause. Just as you have the right to pay the loan off early, the lender retains the right to call it due early. This depends on several factors, your payment history,if you are in default, ect. So, YES, they could refuse.