While the agent sounds both wrong and unpleasant, and it is frankly unprofessional and rude to call a customer by a nickname they’ve explicitly asked to be avoided, I can only say that even when I « think » I know better than the employee of a company I’m dealing with, I’d always try extremely hard to not suggest that I do.

It is humiliating for the person and certainly counter productive and can too easily make me come across as arrogant and annoying (I’m not saying the op was either of those things, just that it can come across that way to the person feeling ‘taught’) so I think it’s best to tread carefully and make them feel that their authority is not being questioned.

I’d personally also avoid citing Flyertalk as authority. It may be a great (though by no means always accurate) source of knowledge but certainly not an official or recognised one so best refer to the airline’s own messages instead.

Again, that said, if that was his words, that agent sounds poor, unpleasant, and wrong and I’d try again every day as availability could easily disappear.