Two years ago I made a single donation via Change.org. I don't even remember what it was about. Nothing until 6m ago when random $10 debits appeared on my Paypal statements. I have checked my Paypal account and found that there was a monthly debit set up. But $10 was not being debited monthly, only at apparently random intervals.
My advice: have nothing to do with change.porg, and pass it on.