Insurance wants to treat some CPAP items as "medical supplies" subject to deductible instead of DME – anyone else dealt with this?

I’ve been on a new employer provided insurance (Tufts Health Plan) for about 2.5 years and it’s been really annoying and confusing to work with them.

The latest is coming up with use of a CPAP machine to treat sleep apnea. I specifically reached out to them to ask about how coverage worked, and was told how my DME (Durable Medical Equipment) coverage worked, which was that they cover 70% of cost, and I have a 30% “co-insurance” payment. I ordered the equipment, and then they applied the 70/30% split to the CPAP unit and most related items (the water chamber, face mask, and headgear) but treated a few items (the hose and filters) as “medical supplies” which meant they were “subject to deductible” and I’d have to pay out of pocket.

I have never had anyone treat any part of a CPAP machine as anything other than DME before, and I’m totally confused by this, and I can’t get them to offer a satisfactory explanation or to change their categorization. Has anyone else dealt with this before? Any advice?