SUBMIT PAYMENT: LOCATE MY ACCOUNT DETAILS

Alright, so I need to settle my bill with Dr. Thompson. I went to their website and it's asking for a client ID number. Problem is, I have absolutely no idea where that is. I've looked my emails, medical records, but nothing! Could someone please guide me? Is there a contact email I can reach out to? Could it be on my last bill? Expedite Payin