I want my Large Shake for Free!!!

So I work at a popular fast food restaurant most notorious for being centered around roast beef sandwiches. During the summer every year, we have a seasonal "Orange Cream Shake" people go buck nuts over this shake, because it tastes just like those creamsicles taste (i honestly think they're way too sweet but that's besides the point). Enter CB, pulling into the drive thru with his nasty smelly truck that sounded like metal being tossed into a blender

Me: Welcome to ***** you can order whenever you're ready

CB: Hi I called yesterday and you guys said you'd replace my shake

Me: Okay, we can get that sorted out for you! what kind of shake was it?

CB: It was a Large Orange Cream shake

Me: What was wrong with it?

CB: It was all liquidy and fucking warm

(this is where i'm like okay buddy that's a lie, I worked all day yesterday and we had our shake machine full the whole time, so the mix never melted in the machine)

Me: Okay... do you have your receipt?

CB: No but I spoke to a manager on the phone yesterday, he said he'd replace it for free

Me: Do you remember what the name of the manager was?

CB: No it was some girl

(at this point all of the managers are listening, and two of them worked all day with me yesterday so we know we never got a call)

Me: Okay you can pull to the window

(I decided I'd give them a medium since I had no proof, but I still wanted to make whatever issue he had right, even though I know he just wanted a free shake)

Me, handing the medium orange cream shake out the window: Here you go! have a fantastic day!

CB: Wait! this isn't a large!

Me: Well since I don't have any proof of your shake being messed up, and none of the managers working remember a call, I can't give you a large, since that's a big shake and we can't just give free food out

CB: are you fucking kidding me?? it's not free I paid for it yesterday and you guys fucked it up!!! I want my large!

Me: sir, you aren't getting a large. I have no proof, you're lucky i've even given you a medium

CB:THIS IS RIDICULOUS! I PAID FOR MY FUCKING SHAKE-

Me, closing the window on him while he's yelling at me because you don't disrespect me in MY drive thru window: Have a great day!

And that was the end. My GM didn't even care, since we still gave him a medium even without his receipt he said we did everything right. I hate fast food.

TLDR; CB wants a free replacement shake from the day before. We give him a medium, and it's just not enough

EDIT: added TLDR