Discovery refuses to reimburse me my money

My husband had a consultation with his cardiologist and we settled the full account before we left. Discovery then still paid the provider directly and after numerous attempts to have them reimbursing me the amount, I still have no joy in getting my money from Discovery. Apparently an invoice done on Excell, stating that account was paid in full, is not acceptable. During this whole Discovery has treated me like I'm a ******** and a ****, trying to get money out of them that does not belong to me. I would also like to add that I have asked to speak to a manager and TWICE I got transferred to staff-level employees after I was told I would be transferred to a manager. Just a warning: should you feel you need to speak to a manager, a Service Specialist is NOT a manager and a Client Relations Manager is not a manager.