Insurence help( betrayed by clinic)

Hello,

I am suffering with hemorrhoids and went to hemorrhoid clinic( assuming it cost less than hospital) and had UHC insurence, When I asked in clinic they said they are in network and I had my surgery. It went well but now after I check the bills it says They are out of network and my bills are around 20k for which i Had outpatient surgery and stayed in clinic for only 5 hours.

When I spoke to clienc they said We dont know whom and what you have talked to, lets negotiate with billing team and asking to pay 13000( 7k is paid by uhc). What I suppose to do now. I am recent grad and international student and I dont have any job. How should I proceed further with them.  Even though they negotiate I cant pay a penny now as I am jobless but they cheated me and I had no proof or evidence. What can I do??