Out of network claims and reduced amount

I have a therapist today that is out of network. I also have a high deductible health insurance plan.

Today, the way my billing works, the therapist charges the insurance company say $300 a visit, they submit the claim, and because I have not yet met my deductible I should be respond for all of it. The therapist sees I have not yet hit my deductible, and then sends me a bill for say $150 till and I pay in cash. They’ll do this till I hit my deductible, which then once I hit, the insurance company would pay say 70% of the $300 being charged – I would be responsible for my coinsurance.

My question is – how are they offering this adjustment?

The issue I’m running into is now my therapist is going out on their own and no longer taking insurance. They are providing me a bill, but the rate is only the $150. I can submit that to my insurance company, but it will now take much much longer to hit my deductible.

Can anyone explain what my original provider was doing and how I can advocate for my new provider to do the same?