What a minute... 5 previous unpaid visits?! This sounds like abuse!
How is it that a patient can be seen that many times without any payment? We document the patient's promise of payment,by the date of their choice.. we offer them to post date checks, but we will not see a patient if there is no honest effort to pay.
Any arguments? Ask them when the last time they pulled up to a drive through, gotten a meal without payment? Show them the payment agreement that they signed in your office when they first filled out new patient paperwork.. explain to them ITS A LEGAL AND BINDING CONTRACT.
If you are in a bind, then perhaps you have no accomodations within a certain time frame, and they can go to their local urgent care facility for this accident, then you will be in a position to send that letter, or make it clear there is no free fast food given at the joint.