i don't even know what to say other then, why? why the fuck would you use a web wallet to recived that kind of money?
If xmrwallet really is a scam now and the owner reads this and have any shred of dignity, please give the XMR back, you have probably scammed more than enough by now.
i'm sure this is not what you want to hear, but xmrwallet.com is 100% a scam. sorry, but your money is gone.
The first time they wanted to send XMR, (due to my own problems, new computer without the GUI installed yet or synced) I created a wallet on xmrwallet. I've actually used this site many times in the early days of monero and never had any problems and until recently i thought it was still trustworthy.
you thought wrong because xmrwallet definitely has been taken over by scammers at some point, check this:
https://bitcointalk.org/index.php?topic=5540097.0Also I was not on the phishing clone that I read many stories about, I take security as serious as I can and I have the address in a text editor that I've had backed up for years. I still have the page open several days later, it is the correct page.
it doesn't matter how seriously you took your security when your keys are in the hands of others. i don't want to make you feel even more shit about this, but you literally donated the money to them.
400 XMR is a lot of money, i hope you can recover from this.