Scammers can use the Telegram mobile messaging app to connect with a potential victim if they already have their phone number in their contact list. Do Not Call rules dont apply to encrypted messaging apps like Telegram. Criminals could use such a service to target unsuspecting users. Users should be careful when approving new contacts, even if theyre a friend. They should also review the apps default settings and check to see if they can prevent the app from capturing their address book.”]
Source: https://grahamcluley.com/telegram-scammers-stored-contacts/