Customer offended at the amount of compensation I offered

I take inbound calls for a big box retailer. Our queue is normally at 0 or 1 (30 if it’s busy) and I take maybe 5 calls an hour on average with several several minutes between each call. But since COVID, the queue regularly hits 16k each day so it’s back to back calls, no time in between for 10 hours straight. So I’m already stressed out and so riddled with anxiety that I start shaking really bad when customers start yelling.

Anyway.

This was yesterday and the calls were extra horrible for some reason. Almost every single one was yelling or abusive or just wouldn’t accept my answer. It was about 20 mins until the end of my shift and I get this guy.

Customer: I placed an order for pick up today and I just got an email it was cancelled. Why?

Me: So it looks like this item is currently out of stock in the store so it had to be cancelled.

I would like to notate here that the order in question was for one singular box of brownie mix for a total of $2.37

C: So…that’s it? You just cancel it?

Me: Well, yes, sir. Your local store does not have the item and cannot fulfill it so it had to be cancelled.

C: Okay but I really needed this item.

Me: I understand. I can check other stores around you to see if they have this item in stock.

C: No, this is the only MYSTORE within 50 miles. I placed this order because I really needed it tonight! Now you cancel it. That’s not right.

Me: I really do apologize, sir. We would have loved to fulfill this order for you, but unfortunately we don’t have the item.

C: And now…what? I have to look around at other stores to see if anyone else has it?!

Me: (trying my damndest not to sound condescending) Yes, that would be the next step since we do not have this item in stock.

C: Well I want to be compensated for this. This isn’t right! I needed this and you can’t just not give it to me and not compensate me.

Me: Sure! Let me see what we can do for you.

Now, for compensation, we have some leeway when deciding what type of promo code to issue. We have 4 different ones, starting at $5 off to $25 off. We use our best judgement here

Me: I can offer you a $5 off promo code for your next purchase.

(Silence)

C:…five dollars? FIVE DOLLARS! That’s what my inconvenience is worth to you? Five dollars?!

Me: I’m sorry you are not happy with that compensation. It is double the amount of your order, and the highest I am able to go.

C: Get me your supervisor. Five dollars. I am worth more than that!

While catching my supervisor up about the issue, she agreed that $5 was more than enough and she would not have offered anything. The call was just so ridiculous and pointless, I ended up clocking out 10 minutes early. I just couldn’t do it anymore.