Is Membership the same as PREMIUM? What's the difference?

They're two different products, and they're easy to mix up because both come in two options.

Membership is a coin reward program: coins straight away, then daily coins for the length of the option you chose (Weekly or Monthly). It gives no in-game status — no Premium servers, no XP bonus, no queue skip.

PREMIUM / PREMIUM PLUS is an in-game status: Premium servers, the queue skip, nickname colour, daily silver, and with PREMIUM PLUS the XP, crafting and Tool Cupboard bonuses. It gives no daily coins.

The practical difference
• Membership can be bought as a subscription with auto-renewal, so it can renew and charge again. It can also be bought one-time.
• PREMIUM and PREMIUM PLUS are always a one-time purchase for 30 days. There is no auto-renewal.

So if you're looking for where to cancel automatic renewal — that only exists for Membership.

You can hold Membership and PREMIUM/PREMIUM PLUS at the same time, they don't affect each other.