Claim not paid in full

What a mess!!! I was admitted to the hospital for a bio-scope and according to my knowledge, the medical plan I have has an unlimited hospital plan. The doctor advised that I need to pay in cash and I will claim from Discovery due to the policy that they have implemented. I claimed the money back from Discovery and they only paid a third of what I have paid. I called to enquire about their decision and I was told that the doctor used the wrong code and Discovery pays a certain fee, not the whole amount. The explanation I got was unsatisfactory and unhelpful for me to understand. I still don't understand why my money was not paid in full because the reason I was admitted to the hospital for the doctor to do a bio-scope. I literally paid the doctor and Discovery paid the hospital. I DON’T NEED ANY EXPLANATION NOW AND I JUST WANT MY MONEY BACK.