They aren't going to "make a deal" over the phone to give you more than you're entitled to. Cuz the person you're talking to 1. isn't authorized to do that, and 2. this could lead to abuse or more liability than they want to take on.
See, if they don't make any promises to you, they don't take on liability. It they receive a couple defective rounds from a single customer that month, they might send them a free crate of ammo. Woohoo, everyone's happy. Or.... they might receive 2 defective rounds from 20,000 different customers that month. Doh. So they start replacing the defective rounds, only. Which is all they're really obligated to do.
If they start making promises to certain customers over the phone, then everyone else will also expect the same treatment.
Then there's the potential abuse issue. A setback round isn't exactly difficult to make yourself. If limited, sure, they'll probably take care of you. But if they get a lot of setback rounds and they're suspicious, it's much better if they haven't made promises.
In general it's better to just send back defective stuff with the product ID and see what happens.