<prompt> Human: Had a minor medical procedure done last year, was billed about 600 for it under my insurance deductible, I paid the bill in full in March 2-3 weeks after receiving the first bill, and never heard anything more from the medical office.Three weeks ago, I received a letter from a collection agency stating that this bill was an outstanding debt. Obviously, I first double-checked that the check I paid to the doctor was actually processed by my bank it was. Then I called the doctors office and talked to them. Their confusion about my name when I first asked them about it led me to guess that they had somehow confused me with someone else with a similar name. But they verified on the phone that I did not owe anything and that theyd cancel the collection. I also asked them to send me a signed letter stating that I did not owe this debt, which the receptionist I spoke to agreed to.I waited for a couple of weeks to get the letter and never received it so, since the clock was ticking, I responded to the collection notice by sending a letter stating that I did not owe this debt. I sent it via certified mail.Today, I decided to check the USPS tracking, and I discovered that the certified letter I sent to the only address visible on the invoice I received was refused by the recipient and would be returned to me.The doctors office assures me that they would contact the collection agency. But they also assured me that they would send me a letter, and they didnt. So Im not sure how much to trust them.No idea what steps to take now... I feel like I took all the correct steps, so what else can I do to protect myself? Note: Im still within the 30 day dispute period  <response>: Hah! Aka, the LA LA LA NOT LISTENING method.Send another letter, informing them that this is not your debt and therefore they cannot attempt to collect it from you.You can include copies of the letter from the doctor if youd like.Either way, since they wont accept certified mail, you can send one certified, one regular.Any willful violation of the FDCPA carries a 1,000 fine. Youre welcome to remind them of this fact. 