Unfortunately, Bitcoins once stolen can not be recoverable unless you catch the thief and force then to send back your bitcoins. That being said, no one can help you hear recover the bitcoins apart from trying to point out what could have happened.
I have questions;
1. Are you sure the address in the bitcoin wallet is the one you sent your bitcoins to?
Some clipboard Hijacking malware can change the address you copies to the thief's address just as you are about to paste it in the receipt address field
Check your blockchain wallet to confirm if the address generated is the exact address you sent money to and then check the transaction history
2. Did you store your login credentials and 12-word Back up phrase in a safe place? If someone or malware gets access to your 12-word backup phrase. The thief can import the your addresses to other wallets like Electrum, send the funds without any need for email authentication.
Bad news to OP, My speculations was that OP was being a victim of phishing a malware that detects the important details of wallet. He had not been made any information regarding on the transfer like a 2wayfactor authenticator so it was probably able to get all the details of the wallet.
Other thing is the glitch of the platform he was transferring with btc. There are some glitches for all platform could not be called perfect and always there are flaws in it that coulr be discover over time by its users.
Again, my speculation was all about that OP was a victim of phishing for the culprit has done transferring btc to other wallet addresses. Someone has done the transfer of course.
Poll
