2nd req for validation. What next.?

Hello everyone outhere!
So, I send Caine and Weiner (which I think is a CA trying to come across like a law firm) a CMRR requesting validation of a debt they are trying to collect from me. About three weeks later they called me again and I told them they needed to respond to my request for validation They claim they never received the request to which I responded that I had a signed returned receipt. They did not believe me and wanted me to tell them who had signed the receipt. I refused as I did not feel I should have to provide them with that particular info. I hung up on them when the caller started getting aggressive, swearing to file suit. On the day before the 30 days were to expire, they faxed me a letter (my phone and fax share the same line and they figured it out when I wouldnâ??t answer their calls) again threatening to file suit. On the following day, I sent them the second request for validation via CMRR and via Fax. If they fail to respond within the 15 day allowance, which will be Nov 13th , what would be my next step? The debt, by the way, is of an insurance company with which I did business for at least 12 years. This past summer they had not billed me for renewal of a liability policy so I called and was told that they were having problems with their billing system and that I should get a bill within two weeks. When that did not occur, I looked for insurance elsewhere. Now, they claim they did send a policy and several bills. I never received them. In fact, I never even would have known of Caine and Weiner because after I researched for awhile, it turned out they had been sending all correspondence to a former address. And I feel certain that this is where the insurance company was sending their correspondence as well. They apparently failed to update their records to reflect my change of address. Iâ??d moved from that address over a year ago. Would appreciate any feedback.
Thanks,
Challenger