Managed To Lose That Sale Real Quick

I am out shopping for home needs. I need a microwave and see one for 75% off. I grab it and head to check out. When it’s scanned, it comes up at full price. 

Me: “The microwave had a sign that said it was 75% off. Is it still on sale?”

Cashier: “Let me grab someone and I can go check real quick.”

She grabs her manager, and the manager says she’ll go and check it. While we wait, the cashier scans the rest of my items.

Manager: “The sale ended yesterday. We just haven’t taken the signs down yet.”

She walks away.

Cashier: “Your total is [total].”

Me: “Please take the microwave off.”

The cashier doesn’t know how to do that, so she calls her manager back.

Manager: “Why do you want me to take it off?”

Me: “I don’t want it anymore.”

Manager: “Seriously?”

Me: *Pauses* “Yes?”

Manager: “So, you want me to cancel your order?”

Me: “Just the microwave, please.”

Manager: *Rolling her eyes* “You’re seriously not going to buy it?”

Me: “Are you going to honor the sale price since the sign was still up?”

Manager: *Scoffs* “No!”

Me: “Then no.”

She rolled her eyes and took it off.

Later, when I checked online, it was still on sale, so I made an order.