The Exchange where I've created account
is it my mistake
what's you thought about it
and how i make my account safe
That will be the exchange responsibility because they need to protect their member from the hacker or from the attacker that comes to their site. You should report it to the support system so they can investigate your account and they will check your log files to see who are login into your account. You also need to check on your computer if whether your computer is affected by the virus or trojan or malware that stealing your account data.
To make your account safe, you should follow all of the things that the exchanges suggest to their members, including to activate 2fa, email verification in login, and withdrawal. As long as you already activate everything, you don't have to worry, and the next thing will be the exchange job to secure their site.