Am I being treated fairly, or am I overreacting?

Nicki

Are you a PA or equivalent whose role is to process the paperwork for sales generated by a sales team by any chance?

If that's the gist of your role, I'm not completely surprised your manager thought you were deluded for claiming sole credit for an uptick in sales. Whilst a small pay rise may have been merited, it sounds to me like you either need to move out from a support role or recognise that other roles are more highly valued in the workplace. Good admin support, whilst important, isn't in reality all that hard to find.