Nokia Lumia 520 isn't showing messages

I've looked around but can't find any available info on this issue. The phone is only a month old and I only encountered this today. The phone vibrates and shows that I received a message, but when I enter the messaging app, it doesn't show the new message. Also when I send a message it doesn't show the message that I just sent. I took out my SIM and SD to see if that was the problem and it worked for a couple hours and then broke again. Any help would be much appreciated

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