It's important to keep a working and up-to-date phone number linked to your Telegram account – otherwise, you can lose access to it. You can move your account to a new number even if you no longer have the old one.
To move your Telegram account with all your contacts, cloud chats, groups, as well as your username and blacklist to a new number:
Note: Make sure there is no existing Telegram account connected to the new number for this to work. If there is account there, please delete this other account before starting the transfer.