Is the additional amount paid to the bank, which is said to cover the bank's expenses and not be interest, considered usury (riba)? And what should one do in this situation?

If the additional amount is in consideration for the bank's effort in procuring the cars, then it is permissible as a wage for a lawful service. However, if it is in exchange for lending the buyer the price of the car, then it is explicit usury (riba).