Welcome to Vodafone Community
Which phone model are you using?
What are the size of the discrepancy ?
When did you upgrade? I ask as the phone can take a few days to settle after it indexes.
Try turning it off and on to soft reboot it.
Although a last resort if this was my situation id do a back up and perform a factory reset.
After any major update, it is always recommended to do a factory reset. This clears out anything remaining on the previous software and clear any bugs.
Providing you have backed up, your applications and other content will automatically be restored.
The reset should sort this out for you, but if there are still issues, please come back to the forum.
I've done several updates without the need for a reset and I'd say it's no longer a routine requirement and only necessary if there are serious performance issues.
As Lee says, it would be helpful to know more about the discrepancy. If you go into Setting|Storage, do the used and free figures add up to the total of the device (bearing in mind that some goes in the formatting process - my 64gb sd card only has 58gb of usable storage, for instance)?
11.16 of 16gb usable sounds about right for the total less the operating system and any files/apps you've added yourself.
In Settings|Storage, you should see the total space on the device and also the space used and the space remaining. The last two should add up to the first one (ie, say 6gb used + 10gb remaining = 16gb total), less the formatting overhead.