And the wallet was not emptied, with more than 100 BTC left not taken, Weird!
There's a possible explanation for that. They stole from an old copy of your wallet. Since then you've sent coins to other people (normal spend transactions) and the change has gone to new addresses (and corresponding private keys) that are not present in the old copy of the wallet that the thief has. So consider where you backed up your wallet in the past.
I had an email sent to me with a withdrawal confirmation at 21:44, that i tried to cancel but there was an error.
How did you try to cancel the withdrawal? Don't tell me you clicked on the link in the email?!! If you did that you CONFIRMED the withdrawal instead of canceling it. To cancel the withdrawal you do nothing and ignore the email.