How to Prevent your Telegram Account from being ‘Hacked’
So here’s what you do to make sure the flaw with SS7 doesn’t affect you.
Enable two-step verification, via Settings > Privacy and Security > Two-Step Verification. You’ll need a reliable email address and a strong password.
My advice would be to use a service such as LastPass, 1Password, etc., to generate and store your password, or just grab one that’s generated from here, set it, then forget it until you need to log in again, and reset your password.
Check to see if you have any active sessions and terminate those which look unfamiliar or for places you’d feel comfortable from logging off of just in case, as not every device can use Secret Chats (which are wiped when you log off or uninstall the app).