I'll say this: Grabbed a free month of Prime through Google Play. Went to cancel it before it charged me again and I had so much trouble figuring out how I decided that I couldn't be the only one and ended up Googling it.
You couldn't quit in the Google Play Store. It wasn't even listed.
It wasn't any form of subscription or listed as a membership on Amazon.
You couldn't end it by following QR codes or links supplied to you on Amazon itself.
It wasn't in your Amazon profile or Google profile.
The ONLY WAY to cancel it was by scanning the QR code, following the link, clicking on a "Contact Support" button, clicking on another button under "Help Topics" that said, "How to end your Prime Membership", and finally you were taken to a page where you could actually end it. Obfuscated like a motherfucker.