That would not be your phone, but your carrier/service provider. It happens all the time. Their systems will have some sort of hiccup and poof you can get the same message 2 times, even 20 times (that is when it gets annoying), or even more fun is when you don't get any messages. For days, and then they all come in at once. My phone went off for hours one day. Had to just turn the sounds off and let it run its course. LOL
Try restarting the phone (turn it off and back on) sometimes that will help resolve it. Otherwise, if it continues for more than a few hours, I would contact your carrier/service provider.