7% Saline Prescription and Medicare Part B payment quandry

My husband is 81, diagnosed with MAC, and has been on the 3-drug regimen for 2.5 weeks. He uses a nebulizer 2XDay with 7% saline.

Problem: Humana won't cover the saline prescription because they say it is covered under Medicare Part B. But, when filling the saline prescription the pharmacist can't get Medicare Part B to work. Our secondary (not supplemental) health insurance Blue Cross/Blue Shield says (thinks?) it needs to be coded as a durable medical, which neither CVS nor Medicap will use. (It seems to me that while the nebulizer is a durable medical; the saline is more a prescription.) In the meantime, we are paying out-of-pocket for a saline prescription the pulmonologist and all others say should be covered under Medicare Part B. Anyone else had this experience? How was it resolved? Many thanks!