iphone 5s fails to make safety backup

I am looking for a solution for a problem that has been annoying me for a while now.

sinds june 13, my iPhone 5S has not been able to make an icloud safety backup anymore.

I do not know why the backup fails everytime because there is no error message which might help finding the cause for this problem. It only tells me the safety backup has failed. (apple: suggestion, include an error code or whatsoever to help the user fix the problem!!!)

I have tried many many things already. I have posted about this on the ask different superuser site. And also wanted to ask my question here.

I therefore completely copy-paste my ask different question here:

my iphone5 cannot make any backups anymore. My last backup is from june 2015. I have checked if:

• I have enough space in icloud (about 4,6 gb)
• the size of the backup (approximately 790 mb)
• removed many many photo's from my iphone

followed these steps:

• turn off icloud drive, reboot, and turn on safety backup again (no succes)
• turn off icloud, reboot, and turn on icloud again (no success)
• sign out of icloud. turn of phone, turn on again and login to icloud again (no succes).
• removed my latest backup in icloud (which turned of safety backup) and turned on safety backup. Again with no succes.
• performed soft reset (home + power button) (no succes)
• emptied my complete foto library (although the icloud site clearly tells me that my photo's do not count for the safety backup)

And what makes it even worse is that the iphone reports no error message telling me why my backup failed.

How can I make this work again?

sites I already read / used:

iPhone 5 backup to iCloud not starting

Can't backup iphone to icloud

in dutch:

http://forum.iculture.nl/f147/icloud/f148/icloud/126819-geen-reservekopie-meer-m aken-icloud-iphone-5-a.html

I am lost with how I can get my icloud safety backup working again. Anyone with a solution on how to fix this?