My iPhone 5 shows My Number as Unknown?

I can't activate my iMessage or my FaceTime. When I go to Settings>Phone "My Number" is Unknown. When I plug my phone to my computer, on iTunes' summary it says "Phone Number: n/a" I can never change it an I think that's the reason why I can't activate my iMessage and FaceTime. I've reset my phone several times, deleted content and settings, took out my sim card and put it back in but it never works. I've tried turning iMessage on and off several times and I've waited for hours but it says unsuccessful. I've tried to go Airplane Mode then turn it off and go to Settings>Phone but I "My Number" still says Unknown.

Go to settings, message setting, imessage, turn off imessage, then turn on. It will validate your phone number.

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