Product: Credit card or prepaid card

Synchrony unilaterally closed my account. I have been a customer for many years. I have exceptional credit scores and payment history. I used the card as my primary payment tool. 
Synchrony closed without warning, stating " payment and unusual purchase history on your credit account that Synchrony deems may be indicative of future intention not to pay ''. I had been an active user of the account to take advantage of their 2 % cash back program. I paid in full every month and often paid in advance. with some months payments greater than my purchases. In addition, I paid my bills when presented, not at the end of the period. In my life, I have never missed a payment or ran a balance over 30 days on any account. As for unusual activity, I am taking my family on a once in a lifetime trip that costs six figures. I was paying it on my credit card over a four month period in chunky increments. I called Synchrony to alert them to this purchase and pattern and asked for them to put it in their notes. When I had a five figure transaction, I paid the balance the next day. No credit exposure for Synchrony and certainly not indicative of future intent not to pay. Synchrony, for whatever reason, does. When they closed account, my account had an overpayment at $ XXXX. Quite a leap in judgement and a decision that doesn't fit the facts from Synchrony. 
My complaint is that Synchrony has been holding onto my material balance of $ XXXX. In addition, I used their services with explicit purpose to earn cash back rewards. In their unilateral decision to close account, they unilaterally forced forfeiture of my rewards. I had a balance of {$31.00} of rewards coming into the month and then earned {$360.00}. That was earned in good faith and according to reasonable business conduct on my part and explicit foundation of the business relationship. Synchrony 's decision to close is their business but to strip away my material benefit is not in good faith but rather self dealing. In addition, they projected behavior that is not at all consistent with my history, intent or practice. I have called and appealed multiple times and their customer service says they can not address due to policy. This is plainly awful conduct and policy. I am not interested in doing any further business with them but it is not right they can strip away value based on commercially agreed upon activity prior to their projection of intent that differs from actual practice. They have no record or fact of misconduct or bad faith on my part. Synchrony is simply stealing what I earned in good faith and proper conduct and they cite their own policy/terms to justify the theft. I wish to have my rewards delivered to me under the terms of the commercial relationship in good standing, as the account details would clearly show. If they wish to project credit risk, that is fine. However without any misconduct or loss actually experienced over the many years, how can they snatch away the core benefits that the relationship was built upon all the while they profit from my business. Synchrony did not suffer any loss but imposed loss and costs on me. Bad act. Do not let Synchrony unfairly steal from it's own customers.