not sure why this happen ..this quite bad
If it had been a brand new account posting this form enquiry, I would have asked for more information or discard it all together for just wanting to troll without having solid reasons because I must admit that this would be the first time that I would hear or read that blockchain.info wallet was hacked. The unfortunate thing here is that there is high chance that the fund is not coming back and blockchain won't refund you as doing so would amount to them that their platform is vulnerable to attacks thereby either ignoring your message or blaming you for causing the compromise. I hope the amount involved is not too much and its time you move to a more secure platform to keep your coins.