it is a scam, once you sent bitcoin, they have no contact so they do not know your wallet address so they cannot send you your bitcoin back.
~ As a miner, it is impossible to multiply your bitcoin just like that otherwise there will be orphan bitcoin blocks worth nothing found.
~You can only earn bitcoin by 1) mining it 2) buying it 3) scamming people 4) mining alternative coin then exchange it
~This is a scam so do not send your bitcoin.
~If people say it works then they want to scam you because they got scam themselves