Primary and Secondary insurance max allowable question

TLDR at bottom. I just found out I’m in collections for something that happened almost 2 years ago. 2 years ago I was in the hospital with chest pain and while in the ER my heart stopped. Being a rural hospital they sent me via ambulance to the nearest hospital equipped to figure out what happened. After that I got some bills from both hospitals and paid everything. I just recently found out that the ambulance company was out of network and that the primary insurance paid max allowable. I called my secondary insurance and have been fighting them for the past 4 months. The first month was they needed more information and needed the information on my primary. Gave them that and never heard back for a long time. Called back and found out they had the info but nothing was being done with it… Literally the lady I spoke with said “weird I see we requested info, and you got us the info. Nothing is being done and its not being sent to claims” After working with her I was told it was being sent to claims and expect to hear back. Month later called again and spoke with someone else that told me the same story as the first lady. So I requested to speak with a manager got that all sorted out and was told that my $9,000 ambulance ride would be brought down to my deductible around $900. 2 weeks went by called back and was told that it was denied because my primary paid the “maximum allowable”. I requested to speak with someone on this as I don’t understand why my primary paying has to do with my secondary…That was 2 weeks ago so gearing up to call them AGAIN. Could anyone shed any light as to why my secondary would deny my claim as my primary paid max allowable? I understand the max allowable side of things but how does it work between primary and secondary insurance?

TLDR: Was in hospital got transferred to different hospital. Found out I owed ambulance company $9,000. Primary paid some of the bill and the ambulance company was out of network. Secondary insurance is not calling me back and after multiple times was told It was going to be takin care of then told since primary paid maximum allowable they are not paying anything. Why would primary paying anything effect secondary?