We are sorry to hear this. MetaMask is non custodial, so you have to make sure your take care of your security and guard your seed phrase.
Please see our security tips:
Also see how to use a hardware wallet to increase your security:
https://metamask.zendesk.com/hc/en-us/articles/360020394612-How-to-connect-a-Trezor-or-Ledger-Hardware-Wallet