Hospital giving threats for non payment of the overcharged bill

I have admitted my 4.5 yrs son in corporate Hospital for adinoid surgery using office insurance + paid 5k for non covered items, and expectes 5-10% of bill amount paid from my pocket as it is common for insurance holders, however Hospital has overbilled me with some costly used pharmacy item which doesn't cover in insurance without information at the discharge bill time, and they got 50% from insurance of bill amount, and Hospital demand me to pay balance 50% and denied to pay, and they said they will discharge and take legal on me, canu u pls advise will I will be in problem? And also doctor took on table desision and removed additional body parts tonsils without prior notice, what legal can I proceed on Hospital? Kindly guide