How hard can it be to get my invoice.

I am so disappointed with the service I am currently receiving. When I made a booking I was advised that the team will be able to assist with sending me an invoice to submit to my medical aid....Shocking service I keep calling and I'm told to send emails and yet no acknowledgment is given. What do I need to do to get assistance, I keep calling and I'm being sent from pillar to post I have done my part and paid upfront.....send me my invoice!