To all with experience with American Express cancelling all of your accounts - I need your help!

I've been with Amex since 2011 and have had several cards over the years (Delta Platinum, Marriott Bonvoy, Marriott Bonvoy Business, etc.).
I was put on financial review because the authorized user has been submitting more than a usual amount of disputes. Once, Amex explained this to me I removed the AU. During my time with Amex, I have always paid my account in full with only 1 late payment (only 2 days) because of the AU again. Yesterday, a different AU paid a payment to their balance (before the due date) and the payment was returned because a check on their account bounced. Amex immediately cancelled all my accounts.

They left a voicemail for my on my house line and I called them back within 5 minutes just to tell me that they cancelled my accounts. They said they can not reinstate them but I can re-apply for another card with no guarantees that I will be accepted. I asked if I paid off all my accounts would they be able to reinstate my accounts and they said thank you but we can not reinstate your accounts.

With all the years, I've been with Amex I have never made any late payments and my credit score ranges from 770-810.

Any advice on what I can do here will be much appreciated!