I used to have a good experience with Delta Dental...

I used to have a good experience with Delta Dental in my first two claims. However, this time was terrible. My last claim was declined after 9 weeks because of missing an x-ray. Ok, fine. I resubmitted a new claim with an x-ray result as a request. No responses at all to my follow-up email. Finally, I called a representative; and I was told that my claim form missing the dentist's tax numbers? I had never needed to submit it before but now. I wondered how my claim form would be ended up if I didn't follow up. Why do I need to provide that information this time, not previously?