Adult Flu Shots with High Risk Diagnosis

I can't ever get these paid. I submit with the correct V code and high risk dx and the U1 modifier and they still get denied. Any suggestions?

Once again..

more details. ICD is v04.81, the shot is 90658 and the admin code is 90471 for regular ins and G0008 for Medicare.

We don't link to the high risk code for any insurer- most policies either cover it or don't cover it, irrespective of health conditions