“Now, I get cashback from Discover, pay one bill automatically on line once a month, and I’m done.”
And behind your back Discover uses its backdoor deal with Amazon and tells Amazon all about your cashback bonus, without your knowledge.
I cancelled both my Amazon and Discover when I learned of this.
I have my Discover cashback tied to Amazon, too, only I had to proactively accept the service. There was no behind my back and, besides, the cashback is only applied to the Amazon balance if I so specify.
You seem to have made a mountain out of a molehill.