I am locked out of two-factor authentication

Try these in order.

1. Use a recovery code. At the code page, enter one of your ten recovery codes in place of the normal code. Each works once. After you are in, go to Security and press Make new codes.
2. Use your email code. If you turned on the emailed code, choose to send a code to your email.
3. Fix the phone clock. Authenticator codes depend on the right time. Set your phone's time to automatic and try again.
4. Wait out the lock. After five wrong codes the second step is locked for 15 minutes, even for a correct code. Wait, then try once, carefully.
5. Use a trusted device. A browser where you ticked remember this device is not asked for a second step for 30 days. Try it. Then open Security and fix your settings.
6. Ask an administrator to reset it. If you have none of the above, only an administrator can reset two-factor on your account. They clear your methods, recovery codes and trusted devices, and the reset is logged. After that, log in with your password and set two-factor up again. Paid members can send a support ticket. Free accounts have no support channel yet, so there is no ticket form for them; the site does not publish a contact address for this. Expect to be asked to prove the account is yours. Do not send your password or any codes.

After you are back in

Turn on your methods again, and save the new recovery codes in a safe place.