billing G0438 with a depo inj. (J1040and 96372) to Gateway Medicare

I have a denial from Gateway Medicare fora depo injection with a Wellness exam. They state we can not bill G0438 with a procedure according to Medcare guidelines. I want to add a 59 modifier to either the wellness exam or the serum and administration of the injection. Do you think this will cover it and which would ou add the 59 modifier to? I have billed a 99212 with a 25 modifier and it's gotten paid with the Wellness exam. Thanks, Bonnie