Order fulfilled and delivered on time, however Amazon Cancelled the order after already received by Customer and has not remitted payment

Order was cancelled by Amazon long after it was fulfilled by us and shipped to the customer. In the few situations where it has taken more than a business day or so to ship, we always received warning notices from Amazon about items pending fulfillment. This was not received, yet the customer has our material ($1600+) and we have not been paid. I've tried escalating, but support keeps repeating the same language about orders being auto cancelled when not fulfilled. We have a connector between our ERP and Amazon that has worked every day for years with zero misses in confirming fulfillment. Other orders the same day, days prior, and all days since have successfully notified Amazon of fulfillment. I've escalated, opened three cases, sent email to Andy Jaffey, etc. to no avail. Has anyone had any luck in small claims court?