A Reverse Karen
In a humorous twist, we introduce a playful term for those who initially exhibit traits akin to a Karen but then undergo a change of heart – the 'Reverse Karen,' playfully dubbed the 'Nerak,' which is simply 'Karen' spelled backward. Fortunately, the OP found themselves lacking the energy to engage in a potential dispute with the company they had made a purchase from, averting a potentially awkward situation.
However, it adds a layer of amusement to the story when we consider that, after nursing feelings of resentment, the OP came to the realization that they had, in fact, been the unwitting perpetrator of a Nerak moment all along.