There's a visible toggle to only show content that's "free for me", so I don't end up accidentally clicking on something that's not included. Plus, everything that's not free for prime members has a big icon attached to it, and it'll actually ask clearly if I want to pay to view it.

The UI is OK, I can easily find my way around it. I haven't used Netflix much, but it was much more of a pain to navigate, even for shows that I was already watching and wanted to get back to.

For shows disappearing, I've always seen a text saying they'd be leaving prime in X days.

I haven't tried Amazon Music, but I did buy a Fire TV stick, and I love that, too. I have a dumb PC monitor with terrible sound and the stick is the only player I've had that managed to only output the sound in stereo, so I can hook it up digitally to my stereo amplifier (through an HDMI toslink extractor I've got off Amazon for cheap). It's also able to tweak the remote signals so that it controls my amp volume instead of its integrated volume control.

I've seen shows that pretend to be in 4K (my monitor is 4k). They look pretty good, but I don't know how to be certain they're actually 4k.

Capital One had (when I was employed there) a process where if someone calls and disputes a Prime charge, they just call a specific number at Amazon and it gets removed instantly. No questions asked and bypasses the normal dispute process.

Call your credit card company, not Amazon.