Need some help deleting

So I have an Iphone 5c and am having trouble deleting text messages. It is saying that I have 4gb of saved messages but whenever I try to delete all of my messages my phone freezes up for a second and then wont allow me to recieve or send messages. If I restart the phone the messages are still there and haven't been deleted. Anyone know how I can get rid of them?

 

Is there any way of doing it without losing everything else on my phone? Can I maybe delete the messages from a backup and restore that?

 

I don't think its a bug i think its trying to get rid of too much at once

 

That works but will take a while seeing as there is so many messages. I think i may just save my contacts somewhere and just restore it.