I've had customers like this, but my store's policy is we can refuse service for any reason, so when they start becoming rude they're asked to leave and aren't allowed to buy anything that day

This is when I get to employ of the greatest joy in my life: "I need to speak to the manager about this!" "That would be me, and no, this isn't a thing that we've ever done. Thank you and have a nice day." The look on their faces is priceless...

Even so i still don't understand how prices of yesterday would have anything to do with prices today as if "yesterday" is an inflexible jackass which cannot be changed in today ....

He's a scam artist and is trying to get you to back down and give in so that he technically didn't steal.

There's a principle called "Fire Your Customer" that holds that a tiny percentage of your customers give you the bulk of your customer service issues and agitas...and that the biggest complainers are also the most miserly spenders. Those customers deserve to be told to take their custom elsewhere, and the business is quite often better off for it.

By chance, do you work at Subway? I know people at work always think the 3 cookie discount is cheaper than it really is.