IMHO I don't see this as something to get nervous about.
I've never come across such a letter. Either amazon is warning you that a ban is imminent, or they have changed the way they deal with return abusers.
Regardless it's nice they are letting you know that you have already been triggered in there system.
-1, that is their warning letter.
Keep returning and you'll be banned for life and have your applied GCs confiscated.
What i have learnt from my online reading about this, once you reach that stage, there is NOONE to speak to about it (no clueless reps can help either) and they will hunt down multiple accounts etc.
I've tried to find updated info about the "lifetime ban/blacklist" but seems like this was a lot more common a good few years ago.
Has amazon got more lenient?
Any specifics on what triggers it?
Ever since looking into this "ban" I always think twice before making an order that I will likely return. Especially since I am joint to someone's prime account and I share my account with others, I'm scared they can all get messed over with a ban.