My solution doesn't help you now, but it may in the future. When I can't get the name and it is absolutely required. I ask for their name because I like to thank people by their name for good service. And then I say I think it's the polite thing to do. Granted this approach doesn't work when the service was subpar.
Normally there is a name of the customer representative or their employee number on every receipt.
Your situation is when your integrity comes into play. An excellent scheduler will go to bat for you, if you've been a great shopper. I used to do all day adventures for the same shop. I have always made sure that I did my best to keep my scheduler updated with my progress.
I cannot tell you how many targets I've tried to accomplish in the last 4 years & the targets were nowhere to be found. They may have made appointments, but decided to quit, go on vacation or flat out ignored appointments. But, because I let my scheduler know what the scenario was almost immediately, I've been paid full fees plus bonuses for 95+% of every single shop.
That said, there are MSC's that don't care and will not pay. These are the companies that you put on the 10ft pole list.
Live your life in such a way that when your feet hit the floor in the morning; the devil shudders...And yells OH #%*+! SHE'S AWAKE!