Sometimes when I’m on with CS, if I let it slip that I know a little something about what’s wrong they take the easy out and send me on my way by regurgitating what I just said as the solution.

The average person doesn’t know anything about Stripe or payment processing. I find it hard to think Amex would steer you that way out of the blue.

Is Amex really saying “here’s a phone number to some third party, resolve it yourself”? Totally unprompted?

I would call in and pretend to be as dumb as possible. All you know is you keep getting charged and you don’t want the charges anymore. The business phone number you have is disconnected. Let them take it from there.

Your best bet is to get in contact with someone who is in sales who can escalate this to an engineer or other more technical person. One way to do this may be to declare that you will tell your customers AMEX is no longer acceptable unless they help you resolve the issue. This may seem harsh but I bet it would work at AMEX and not a VISA or Mastercard