Don't personally have any asset stored on blockchain.com, isn't the site safe from hacks and malwares?
No site is impervious to hacks and malwares. Security is a two way process; The user has to maintain safety when accessing an account, by not downloading unverified applications, avoiding random links, not repeating passwords etc. If one clicks on a malware or downloads a malicious script, their funds can be stolen from any platform.
The platform also has to protect the assets of its users, by using secure servers, regularly checking for vulnerabilities etc.
I asked them and they say for bad screen and errors it is bug you can use App. for money we can't do anything 
Do you mean they told you to use the app if you have a bad screen or error, and for stolen money, they cannot do anything about it (like refund)? Sure It is hack.it is not phishing or virus ,....
security is up there.when you want to login you must use Id and after that they send email with link for that id.after that you must use 2FA code.
Their response is not professional.I think They know about that but because of refund Don't say anything
https://imgur.com/bL0PCUW