Blockchain.info is very known and reputable, and they do not have access to your private keys. There a couple things that may have happened here. 1) Occasionally, their nodes are wrong and show a zero-balance or incorrect balance. You can import your private key or wallet seed into another wallet (or manually check your public addresses on another block explorer) to see if this is the case.

Or 2) your computer may have been compromised, allowing hackers access to the private keys via the browser. Or 3) You gave away your recovery seed or password away in a scam. There have been scams going around where the victim is asked to provide password, then change it. Afterwords, the BTC is stolen using the recovery seed.