I'm not sure why you got the message saying you hadn't filed your tax return yet. The $1,200 looks like either the first round stimulus payment for you or your spouse, if applicable, or $600 for two of your dependents.
You should have received $1,200 for each taxpayer and $500 for each dependent under 17 years old for your fist stimulus, and $600 for each taxpayer and $600 for each dependent for the second one. If you received less than the amount you are entitled to, you will be receiving a correspondence from the IRS to which you can reply and request the missing stimulus money.