It is a red flag when the person that purchased the full fare F/J tickets flew in economy, with pending upgrade requests, on all the same flights from which the tickets were cancelled and refunded. Nowhere did the OP say that the tickets he purchase and refunded were for himself. He could have purchased those tickets for B. Bunny or E. Fudd for all we know. If he purchased tickets for the purpose of increasing his odds of obtaining an upgrade, that is against CoC and results in inventory spoilage and ultimately loss of revenue. While the info that the OP provided makes it appear this is about Citi miles, it is not, otherwise AA would not have closed the account.

IMO, AA also has all the evidence it needs, they are just giving the OP the chance to fess up and salvage some essence of his account. The OP's reluctance and refusal to provide the info AA requested tells AA that he is hiding something and will in all likelihood continue gaming the system at AA's expense. Those who fess up are saying they are wrong and show a willingness to accept responsibility for their actions and as such AA might give them another chance, but understandably will also penalize them to some degree.