Q: The last backup could not be completed

I've been trying for a couple of months now to backup my device (iPhone 5) to iCloud without any success. I've tried all the different "solutions" I have found that have worked for others, but none of them have rendered successful with me. I will list below all the actions I have taken to try and fix this problem.

I must make clear that the iphone has always been running the latest iOS, so this shouldn't be the issue.

1. Soft reset (holding the lock and home button)

2. Deleting old iCloud backups

3. Signing out from my iCloud account and signing back in.

4. Doing a network settings reset on the device.

5. Trying to backup from a different network (wi-fi)

6. Purchasing additional space, thinking that although i had enough space to perform the backup, this could finally solve my problem (it didn`t).

Please note that all my other devices backup fine, it's just this one that won´t backup no matter what I do. And whenever I try to back up the device it just freezes in this screen, never does the actual back up, nor does the blue bar shows any advance.