Is a quartely A1c test covered in the Medicare Supplemental plan.

 I am on Medicare with a BCBStx medicare supplemental. I have type 2 diabetes. BCBS seems to have difficulty paying for my quarterly A1C test. I went to look at the coverage, but the website has difficulties and for some reason, wont show my coverage details. Hence, this question.

Are A1c tests covered by the Medicare supplemental plan? If so, how often? My doctor recommends quarterly A1c. But, BCBStx for some reason has not paid my test from last July.