Speech Beginnings, PLC

I contacted this company for speech therapy for my daughter on the recommendation of her doctor. First they said that they don’t accept any insurance. I decided to do the difficult task of dealing with my insurance company directly and filing an out-​of-​network claim so that my daughter could have services here.
I sent them the blank claim form, which is a very standard and routine form that asks for the provider information and list of the services provided, dates, costs, etc.
First the owner of this business told me that she won’t be able to fill in the part of the claim form that asks for the business tax ID because one time some insurance company sent them some incorrect tax document, and now their «accountant» advises them against giving out their tax ID number, and if this is a problem then I should go elsewhere.
This sounded a little suspicious to me, and very off-​putting, but I agreed to contact my insurance company and got approval in writing from them to accept the claim form with no tax ID.
Then when I told Speech Beginnings that my insurance company would accept the form with no tax ID, they told me:
«I shared the insurance claim form with my attorney who cautioned me about signing any health documents requiring a physician’s signature. Therefore, on the advice of my attorney, we will not be able to assist you.»
After that, they stopped responding to my emails.
Note that the claim form does not require a physician’s signature, and what kind of attorney would advise a therapy provider not to sign a routine insurance claim form?
First they can’t give me their tax ID number because some insurance company once sent an incorrect tax document, and now they can’t sign a piece of paper that states that they performed a given service at a given date and time? Something is very suspicious about this company.