1- Never, and i thank to the god  my wallet never been hacked since i know cryptocurrency
2- never
3- I don't know exchange will pay you back or not,but you can contact customer service
and it has low potential (to get your money back)

My tips is, keep your wallet secure
trade on market with high security with 2fa authenticator. (its the best way to avoid your asset hacked)
Don't input your private key without any reason (join airdrop,bounty).
Please double check the website before you wanna login on website, there is so much fake site (BE CAREFULL )