provider is billing me for 1k but EOB says I owe 0$?

So today I saw that I’m being charged over 1k by my therapist office for appointments over the last year, but it’s not making any sense to me why I’m being charged this and the bill is confusing me.

For context, I’m covered by two plans, 1. my own plan I get through my employment as a grad student (my universities student health plan) and 2. I’m 23 and still on my parent’s insurance.

While plan 1 should be my primary insurance as it’s under my name through my employment, my therapist office requires that my external (non university, #2) insurance is listed as my primary. This office is out of network for my parents plan, so I get an EOB saying they denied my claim and I owe like 300-400$ per session. In the spring I called the billing office of my therapist to make sure that this was normal, and they said it was and that it would go to my secondary insurance (plan 1) where it should be fully covered. As this office mainly serves university students they are super familiar with this plan and that mental health service office visits should have a 0$ copay, deductible waived.

With that, I finally receive my EOB for these appointments from insurance 1, the break down basically says that there’s a discount of about 200$ per appointment and they paid about 120$ for each, and that I owe 0$. This is all great until I checked and saw the 1k charges on my account from the therapist’s office. The cost breakdown of this basically says that my primary insurance (plan 2) denied my claim, and that my secondary insurance (plan 1) paid the 120$, and they’re charging me for what was listed on my EOB as the “discounts.”

I’m super new to dealing with insurance stuff and I’m not sure how to proceed– it doesn’t seem like I should have to pay anything due to my EOB. Any guidance on what could be happening here/ what to do? I cannot really afford the 1k right now and only went to this therapist as I was told it would be fully covered.