Years ago Medicare used to require DC's to have xrays to support need for treatment, but they did away with that 10+ years ago. When our local carrier switched last year we had the new carrier denying claims for xrays. We had to call and actually got the Congressman involved. Eventually they fixed the problem. I am not aware of Medicare changing the requirements for xrays for DC's so I would call back and ask them to point you the to CMS ruling that states xrays are required. It would be in the LCD's and they are posted on line, so make them find it and point it out to you.
Good luck
Michele