You need to call the agency immediately!...before you make things worse!
Call the Rental company immediately and speak with the manager, this will determine if you need to work a payment plan or seek legal advice, because the biggest mistake you have made was abandoning the vehicle!...you may even have to tell them that your vehicle was stolen, I mean were the police there to make an accident report or something! if they did..call the rental company immediately and tell them where the vehicle is! they can send there towing guy to go get it..if not they can charge you for grand theft auto, because right now, you are considered as being overdue on your return, and if they don't here from you... they will call the police and report there car stolen!...I tell you this because I'm a manager for a major Rental car company here in Orlando Florida..some customers try to pull this stunt all the time especially when they have un-authorized drivers such in your case, but we want to at least recover our vehicle, either way all of our vehicles are covered with or without your insurance or personal finances but if it is lost..we have to file it as missing or stolen.. and if someone else has picked it up you will fork up the bill for the whole vehicle! forget about $700 dollars your going to pay $27,000 if you don't recover that vehicle.. don't make a difficult situation worse be a man and take responsibility for your action...if this was done in D.R. your passport or license may be confiscated and suspended, to prevent you from leaving the country...either way seek legal console your going to need it especially if that car is missing! well good luck.!