If you inadvertently bought two memberships then you don't lose out as they stack to kick in one after the other.
Auto renewal shouldn't buy additional memberships until necessary - i.e. all stacked/queued memberships get used up.
But if you want to switch it off you can do so yourself via your My 48 account page on the website (not sure if you can do it via the app but at the moment you probably can't log into the app at the moment anyway due to a system fault).
If you need any unused memberships refunded then you'll need to contact 48 support.
See the link in my signature below.
Hope this helps.