Why does my phone not tell me I have a message?

[AC Question]

I have a Galaxy Ace Style and it has recently stopped showing me when I have messages. Like used to when I got a message, my phone would vibrate and show the message on the screen (even if it was locked) and when I would unlock it there would be a little message symbol at the top. But today it hasn't done that. It won't vibrate or even show I have a message unless i'm on the messages to the person I am texting.. I have made sure the time and date are correct, which they are, and I have tried to take my battery out a leave it out for awhile.