Cryptocurrency transactions are irreversible. If you send cryptocurrency to a third party, you cannot reverse it or stop payment. When you send cryptocurrency to a blockchain address, you must be certain of the legitimacy of any involved third-party services and merchants, and only send cryptocurrency to entities you trust.
Pro tip: If it sounds too good to be true, it probably is.
Coinbase has no official presence on the Telegram messaging platform. All varieties of scams can be found on this platform that target Coinbase users, including fraudulent payment bots and giveaway scams.
Read this blog post for more information on Telegram scams.