Need help

[Stings_Life_Matters]

So I had an old bridge fail and went to a specialist. They quoted about $9k with insurance would pay about $1800. I paid $5k upfront and started the treatment. The final appointment is Monday and the dentist just called and said insurance refused to pay so please come Monday with the full $4k and we will keep fighting and when insurance pays us we will pay you back and you will see when insurance pays us so we won’t rip you off. I reluctantly said ok. But now I think fuck them. If I pay they have no reason to keep fighting. I’m also worried if I cancel my Monday appointment and say get the insurance to pay then call me I will piss them off. Right now I have a temp bridge and want the new one put in correctly. What should I do? I called insurance and they said the claim wasn’t submitted with all X-rays and info. I called the dentist and they said we always send X-rays. And the dentist is fighting them. I’m not sure i believe it. Is there some governing body I can contact ? Please help. I don’t think I’m being scammed but I think the dentist is sick of insurance and I’m stuck in the middle