Deleting text messages reappearing problem

I'm using an iPhone 4S with iOS7.0.6 installed.

The problem I am having is that I have way too many text messages and it is currently taking up 4gb+ of memory space.

When I try to delete some of my older text message conversations from people I haven't contacted in a while, it allows me to delete them perfectly fine but if I exit from the messages application app then go back into it, it deletes all of my conversations. If i then reboot the phone, all text message conversations reappear, including the ones I'd previously deleted... any help?