Ian says: "That's the whole story... if you do a search online for "amazon banned", you'll see this has happened to many people: some total scammers (good for Amazon!) and many just normal people like me who got rounded up inappropriately."
I just googled "amazon banned" and read the stories. Wow. I'm stunned. It seems to me that they would at least give you 1 warning. But in all the other cases I read about, there wasn't a warning. Your story is consistent. You must have returned a rather large amount of expensive items. That seems to be the common theme. It makes sense to say, "1 more return and you're banned" or something like that. Rather than ban customers, why not revoke return/exchange privileges? If this happened to me, I'd be tempted to go over to the dark side, de-drm everything I had and acquire whatever I wanted from the darknet. Nuts!