I had an exchange summer but left with an huge medical bill

Im not certain how insurence works in the usa , although I know an bit about it , during my exhange program , my agency gave me free insurence , upon arriving at my program I suddenly started having bad stomach cramps and UTI symptoms , I went to urgent care and found the issue , it were something minor , mainly female issues ( infection ) along with an overian cyst but nothing really serious. When my problems got worst , I went to the hospital as advised. They did around 4 tests and kept me in for an few hours. The results wasnt anything really bad but something that could occur at anytime. Upon returning home , Ive been charged $16,189.07 and my insurence is refusing to pay any of this money , claming my problems were pre exisiting yet any woman at anytime could get an infection and there were no way of me knowing I had an overian cyst. I cant afford that amount , being an student and working an part time job.