CREDIT ONE BANK DO NOT HAVE AN ACCOUNT AND TOOK MONEY FROM MY CHECKING ACCOUNT LAS VEGAS NV

Yes if you don't have any business with Credit One and there was a debit to them, then yes this is Fraud.  BUT I can just about guarantee you that Credit One didn't just pick you out at random to hack your account and withdraw $400.

What does this mean?

It means that SOMEONE used your information and gave it to Credit One,  and that was enough information for Credit One to submit the payment to your bank and your bank to approve it.   This is called Identity Theft and you need to contact your bank ASAP to dispute it.  You should also use this time to review all of your other accounts as well as your Credit Report in case there is something bigger.  

If you suspect Identity Theft you need to file a report with your local law enforcement and put a freeze on your credit reports by contacting the Credit Reporting Agencies.