My iphone 4s is having strange memory usage?

It seems as if i have less and less memory every time i use my phone and i delete more stuff and it doesn't seem to affect the memory… Its a 16 gb iphone 4s so with the stuff its suppose to have on it 13.5 gb… Before i had more videos, pictures, apps, and music… And i wanted to add a new album i just bought on my phone so i deleted all of the videos on my phone and when i went to sync the album onto my phone it said it didn't have enough space and i checked it said 0 bytes available so i deleted like 200 pictures… And it says once again 0 bytes available… So then i proceeded to erase all mu text messages and some apps… And still 0 bytes available and i find it quite strange, any ideas on what could be wrong?

Added (1). I just restored my phone and now it says over capacity D;

Your iPhone most likely messed up thats what use to happen to mine but all you have to do is restore it and it should be good to go if you don't know how to restore it open up itunes, connect your phone and on the page that has all of your iPhones information there should be a button about half way through the page that says restore. You click on that button and a message will appear saying if you would like to back up your phone which I recommend you do i you have important information, anyways a few more messages will appear just agree with everything and your iPhone will be restored. When you restore your phone will automatically be updated to the newest ios and this process of restoring will all depend on your internet speed.

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