The customer is always right in matters of taste, to finish the quote.
Sorry pal, it’s a tough feeling but you can’t ask for sale prices when you purchased outside the sale period. There will always be folk who buy just before or just after price changes. It isn’t Nothing’s fault, nor is it yours. (How could you know)
But also it isn’t reasonable to ask for any money back. It doesn’t make it bad customer service that they’re saying no, either - it’s just business.