today same case happened to me through telegram.and i just checked his telegram account and found no username then i ask him to provide username so that i can connect him by my other telegram account and he set up his username. after that same process carried and he asked me registered email and sent me 0.8978 fake btc. when i tried to withdraw it seemed need to deposit 0.015 btc to the provided address to verify my account to release frozen balance. after that i tried to investigate and found no twitter or telegram or any other social account of site (https://crypto-core.info) and even i searched on google and all exists a big scam....please be aware and share with your friends.