LaRue,
If the check was fake, your bank should handle this as fraud and they should place the money back in your account. The company Demi Box Ltd may have been scammed by someone who made the fake check.
You definitely need to close that checking account and have the bank monitor it for any bogus checks coming back for collection.
In order to get or make the fake checks, someone had to get your bank routing ID and your checking account number....Perhaps from a check that you wrote to them, or the business they work for? Just review who you wrote checks to, and it will probably be an individual or some business you did not do business with on a regular basis...perhaps only once. It could even be someone at the Bank?
The amount of the fake check, makes me think this is an amature job, and likely the idiot used a check printing service to make your checks....they usually put their logo or name on the checks, so you bank should be able to get the address of where the checks were sent.
Never the less this was fraud and your bank should be able to recognize it as fraud and you should not be out any money...however, if checks start to bounce you might have the local DA knocking at your door, so be sure to make the Bank aware of this problem and they can do a lot to protect your financial reputation.
...Rich