Out of Network provider won’t recode bill; insurer won’t specify what CPT code they’ll accept

Grappling with an out of network nutritionist who provided a session on telehealth and coded their bill with a heading that said “place of service telehealth” but a CPT code which is for face-to-face.

Insurer (Aetna) denied coverage because the telehealth visit wasn’t coded with the correct CPT code and didn’t have the telehealth modifier. They wouldn’t tell me which CPT code was the corresponding telehealth codes for the in-person codes which had been used instead.

When I wrote to the provider to ask them to rectify the bill, they said they couldn’t change the CPT codes because they “bill for medical nutrition therapy”. They noted, as I had, that they had already “indicated telehealth as you see” and that they don’t “have an option to add a telehealth modifier”, concluding that “sorry if the bill is not approved but this is the bill I provide”.

I’m sure this is annoying for them because they’re a sole practitioner and don’t have a billing or coding department but isn’t this just part of the cost of doing business?

What should my next move be here?