I don't know what Maryland laws say or what the local rules provide BUT as if you lose it will be for $500 plus interest and court fees, I'd show up and tell the judge or clerk you did not understand that you had to send something in and here you are and you want to defend.
The court probably will reschedule the hearing date. It may condition this on a statement from you that you have a bsis to defend. SO what is your defense?
The services were rendered by the hospital for you and they presumably were performed, and the fact that your health insurer did not pay does NOT mean that the hospital is not entitled to the money.
NOW if the hospital had a contract with the health plan to charge the insurer and not to charge you, that's a defense. Or if the $500 price you were charged is the retail "rack rate" and under the plan the hospital would only get $200 (and yes, hospitals give HUGE discounts to insurance plans) they you should say that is the "reasonable and customary rate" and they are charging $500. Thus your defense might be that you are not the proper party to be sued (the plan is) and/or the fee is in excess of "reasonable and customary" in that the great bulk of fees are paid at the reduced rate, not rack rate. (The term rack rate is one hotels use, not hospitals.)
