if I've created account/wallet on coinbase or any other exchange then my account is hacked and my coins/money lost who are responsible for it
The Exchange where I've created account
is it my mistake
what's you thought about it
and how i make my account safe
Nothing is 100% safe. It's all a question of managing risk. Even having everything offline is a risk in case you lose your private key.
Some exchanges reimburse users who lose money due to an exchange hack, and responsible ones keep the vast majority in cold storage with a minimum in hot wallets.
Coinbase I think is quite good in general, and obviously has a reputation to maintain.
Where you tend not to get reimbursed is if it's a small/disreputable exchange, or anywhere where the mistake is yours - e.g. giving your private key away, software vulnerabilities on your own pc, etc.
Generally just take sensible precautions, be careful with your keys, and don't key everything on a single exchange. A mixture of good exchanges plus some offline storage as well probably mitigates the risk sufficiently.