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Please post accordingly.You should be able to move apps from device memory to internal memory.
For apps,you should be able to go to settings-apps-device memory.Tap on an installed app and you should get that.
I got a similar problem...My Xperis S phone had 19GB of free memory, but whenever I try to install any application it said Device memory is full...I fixed the problem by backing up the phone and then formatting using Factory reset option. After this I restored my backup and everything went fine...
I guess the problem could be due to memory defragmentation..and my phone is 2 year old...
may be this solution will help you..try it out and let me know...