imessage uses too much storage
Hello,
I've got a big problem. I updated my ipod Touch 5g 64 GB to ios7 on thursday. When I was looking in the settings to see the new options and functions, I got to the overview of all apps and how much storage they take. Normally, my 2 GB games were there at the top, but this time, I was really shocked: iMessage used 13,1 GB of my storage although I've cleared my complete history. I noticed that my ipod uses a bit too much storage, but ios 6 didn't show the usage of imessage. I searched for an option to delete these files, but I didn't find an option for that (signing out of imessage and apple id, checking imessage). Now my question is: How can I delete those files, because it takes too much storage and I can't even use them.
iPod touch (5th generation), iOS 7