Dissapearing messages and update freezing on iPhone 6+

I seem to have a problem with my iphone 6+ My phone was low on power and then ran out of power totally. When I finally got to charge and start my phone, all of my messages disappeared and I unable to send any messages out. When you select a name to message to, nothing appears on the "to:" field. When I go to settings and check under messages, imessage is disabled and there is no way to turn it back on. This problem happened before twice with my iphone at the most inconvenient times and each time, apple support was unable to figure out the problem of disappearing messages besides doing a backup and restore.(I spoken to many techs)

I was in a rush that day and instead of doing the backup and restore, I saw that the 8.4 update was available and thought that if I update from 8.3 it should fix the messaging problem with new software. The update goes up until around the 75% mark and just freezes. I tried holding home and power to reset and then I get the "slide to update" screen. Every time I try to update, it seems to freeze around the same point. I tried leaving it alone overnight and even plugging it into itunes to do the update from there but it still freezes.

Is there any way to still back the phone up at this point to recover my pictures and data? I spoken to apple support and they said they could not advise anything but to look for a third party solution.

When I plug the phone into itunes, it shows the breakdown of different categories of data so everything should still be on my phone. The phone shows a 'slide to update' screen whenever I restart. When I try to select backup in itunes, it says that the phone is locked and I need to enter the password to unlock it but when I do so, it goes straight back to updating which freezes instead of backing up.My last backup is about a month ago and I'd rather not lose the pictures and data I had on the phone since.

Anyone have any ideas?

Thank you