Sorry for the travel disruption but hope you enjoyed your time in Jamaica.
Did you check your credit card? I'm under the impression that refunds for downgrades are automatic. For example, I had an F/J domestic ticket and stood by for an earlier flight where I was only able to get a coach seat. The next leg I was able to get in F/J.
Within a day or so, I noticed a pending reimbursement on my credit card where American had issued a credit. It wasn't for the entire difference since I had one flight in F/J and the other in Y.
In terms of contacting AA, best guidance is always to keep it simple and focus on the most important issue. For you, is that the fact you weren't seated together or is it that you paid for F/J and only got it for part of your flight?