Just FYI, cross-posting is against FT rules, but not to worry for the moment - we'll sort that out between the Mod teams.

I think your question is more likely to get answered here, so let's try and make a start.

The Chase agent has partially got it right by telling you to look at the fare code, but we need to know the fare basis (the whole string of letters after the 'O') which will tell us what fare type you have. The 'O' merely defines the earning rate in BAEC or whatever FFP you credit to, which is why it is the same for both Economy Basic and Plus. You are not looking at two distinct classes here - just what services are included within the same class.

Basic essentially has nothing. Plus has free seat selection (for oneworld Status holders ahead of check-in, and at check-in for others), hold luggage and free on the day changes.

BA has a 24 hour cancellation policy, but you may be constrained by Chase's policy here as the agent.