how do I get a "message" (no x out) off my browser screen?

I have a 1st generation ipad. a message has popped up say my device is locked with an 800 number to call. the message will not go away, there is not an "x" to close the window. when I called the number they did not answer like "apple support" or something that would make me believe they are legit. and hung up when I started asking questions of them. I have turned the device off and waited over and hour to turn back on. the message window is still there.