Before assuming the worst, check the two things that explain most of these.
1. Is it a renewal?
Subscriptions and monthly donations renew on their own. Open Subscriptions in your settings to see what's active — something you signed up for months ago is easy to forget.
2. Is it actually one payment?
Click Details on the transaction, then look at Related transactions. One payment often produces several lines: money reserved shortly before a renewal and then taken, or a purchase split between your balance and your card. Several records, one charge.
If it's still not yours
Reset your password. This ends every other session on your account, so anyone signed in elsewhere is signed out. It's the first thing to do, not the last. See How to Reset Your Password.
Write to us at [email protected] with the transaction ID from Details, the amount and the date — as soon as you notice it. A payment you didn't authorise is one of the cases we can refund; see Requesting a Refund.
Check the Notifications page too, under Earnings, Subscriptions and Donations — it often shows what a charge was for.
See If Your Account Has Been Taken Over if you think someone else is in your account.
Need help? Contact support at [email protected]