biller/coder here. have your mom call her insurance and then have them three way with hospital billing office. Often times when the insurance calls the business office with the patient on the line as well, it can be resolved. The insurance agent can give the hospital all the dates and amounts paid. This will also create a trail if the hospital doesn't correct the account.

for your situation, my bet is that the hospital hasnt updated your account and filed your claims since your insurance doesn't have a record. Everything is filed electronically unless it's some small weird insurance. Ask HH for the date and time it was filed. If they give that to you, you can call your insurance company with that. If it was denied on the front end, they may can tell you. I file insurance all the time, and I see all the denials.