You are correct in all your assumptions.
When I followed your instructions about canceling my subscription last time, I simply did not have the "Cancel Subscription" option. This time, the option did appear, and I was finally able to cancel.
And yes, your removal of my Community Supporter status apparently had no bearing on the PayPal subscription, and once the monthly subscription was charged, the status was reset automatically (with no action on your part).
Looking back at the whole thing, the real mystery is this: why did I receive an e-mail back in October/November telling me that my ENW subscription was about to expire and that I should re-subscribe? It was this e-mail that prompted me to re-subscribe (thinking that this was the normal procedure and that I'd have to re-subscribe every month), which caused the double subscription in the first place. You may want to look into the way automated e-mails are set up.