NO FEEDBACK ON INVOICE BILLING - MONTHS ON GOING

I had my baby on 18 March 2018. Months afterwards I received a bill for Neonatal ICU. I queried the invoice. The accounts lady does not answer any of my queries. I have a right to know what have been charged to my account. The days they are charging and why they are charging different fees for the days for my babies stay in ICU. He was not in isolation and the monitors and medicine is charged separately. The credit controller has a terrible attitude and does not respond to any of my queries??? This is insane.