Wiki Medicare/Medicaid secondary: HCPCS services non covered by Medicare paid by Medicaid

[DK47]

Hi,
I work for a community mental health center and most of our services that we render are HCPCS and covered by Medicaid.
My question is: Since the services are not covered by Medicare do we bill Medicaid directly or do we still need to bill Medicare as primary?
I have asked this question several times to our MAC and received multiple answers. Can any one help?