Humana and GY modifier

We have a few DME items we dispense that are non-covered by Medicare. I submit the charge to Humana in the same exact format as what I submit to Medicare. However, Humana continually denies them stating that I am coding them incorrectly. Because of the way they deny it (CO4), I am not allowed to bill the patient.

This is what I submit:

L3100 RT or LT, GY POS 12
L3260 RT or LT, GY POS 12
L3000 RT, LT, GY POS 12 (billed on individual lines)

The diagnosis codes are...

Humana and GY modifier