<prompt> Human: I had to go to the emergency room two years ago. The doctor there billed seperately using Del Mar medical billing company got my correct insurance info from the hospital.Del Mar never once sent me a bill. I had good insurance and assumed they just billed the insurance company, so I forgot about it.Last fall I got a call out of the blue from a collection agent, demanding 300 and threatening my credit. I finally got them to tell me who their client was Del Mar, but they wouldnt give me contact info. Using the name and a phone call to the local hospital, I tracked down Del Mar. Turns out Del Mar billing company billed the secondary insurance without billing the primary. claim was denied by secondary because the primary was in place. I called both Del Mar collection agency back and asked them to bill primary insurance. I asked again for a bill from Del Mar so I could contact my ins directly. Nothing happened for 6 months. Then collection agent calls me again demanding money. Again they tried not to give me info on their client. I dug up Del Mars current info new company name and called them again. They didnt know why the primary wasnt billed wouldnt promise to bill primary insurance. They just said it was my responsibility to take care of. I asked again for a bill so I could submit it myself. Still no bill from them -- ever. Ive not moved in 2 decades and the address they have for me is correct.I dont have 300 to give away, and this is stupid when my insurance company would cover it.I cant apply to insurance Co for reimbursement if I cant get a bill.Del Mar refuses to call off their collection agent, wont sent me a bill, and apparently wont properly bill the primary insurance. Collection agent continues to pursue the debt knowing in writing Del Mar never billed primary ins.What would you do? Can a collection agency damage my credit for an amount that has been in dispute all along? How much could this be lowering my credit rating?  <response>: Sounds like a scam.Other threads usually tell you to first ask for proof of debt and if they dont give it then ignore them. 