trying to get receipt for medical bill, but office won't comply...now what?

I paid a medical bill on behalf of our birth mom. I asked for a receipt be sent to my address. When it arrived it had nothing to indicate my name or form of payment. I could always piece together the story for the IRS next spring by showing the charge on the account, and then showing my credit card statement, but I would prefer one document that shows the fee and demonstrates that I paid it. When I call to explain this I get resistance and so far no one has sent me anything further. Is it birth mom's privacy they are concerned about? I have an open relationship with her, I have statements with her name, I know her date of birth when I call to discuss the bills. What higher authority can I approach to demand a simple receipt for a simple transaction?