GET|MY|YOUR DOCTOR CLIENT ID: WHERE'S MINE?

So, we just need to pay the doctor's bill. Easy, right? Not so fast! The website says I need enter my Client ID, but where am mine? This whole situation is getting me crazy! I've searched everywhere, but it darn Client ID seems to be gone. Perhaps I just missed something? Could I call customer service?? Help! This is truly a headache. Ve