I Need My Client ID

Okay, so I am trying to make a payment for my doctor's bill, but it says I require a client ID. , The thing is I can't seem to find it anywhere! I've checked through all my files and even contacted their office, but they haven't been able to help me with it. What should I do to get my client ID? C
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15