Follow the prompts to associate your account with your new, accessible phone number. This is vital to prevent future lockouts.
Scenario 2: You Have Two-Step Verification (2FA) Enabled and Remember the Password AND the Recovery Email
This scenario is only helpful if you also have an active session (Scenario 1). If you don't have an active session, even 2FA won't bypass the need for the initial phone number verification code.
How it works: 2FA adds a password layer. If you're trying to log in from a new device without access to the old number, Telegram will first try to send the code to an active session. If no active session exists, it will fall back to SMS.
The Challenge: Even with 2FA and a recovery email, Telegram telegram number database still attempts to send the initial login code to the phone number. The 2FA password comes after that initial code is entered. This means if you have no active sessions and no access to the old phone number to receive the SMS, your 2FA and recovery email are useless for the first step of recovery.
Scenario 3: You Have No Active Telegram Sessions and No Access to the Original Phone Number
This is the most difficult situation, and unfortunately, account recovery is often impossible in this scenario.
Why it's difficult: Telegram's core security model relies solely on the phone number for initial authentication. They explicitly state: "Unfortunately, the phone number is the only way for us to identify a Telegram user at the moment. We don't collect additional information about you, so whoever has the number, has the account." (from Telegram's FAQ).