Olympus E-PM2 Memory Card problem HELP?

So I have had my camera for a little less than 2 months. My camera is an Olympus E-PM2 that has a 16GB memory card. I recently took 1000 pictures and found I had 500 pictures left. I put all the pictures on my laptop and I used the laptop to delete about 700 pictures leaving only 300 pictures on my camera. However, when I deleted the pictures off my camera using the laptop, I was hoping it would free up more space but it didn't. I deleted the remaining 300 pictures hoping I would free up more space. However, I still have the same amount. Now I have only 70 shots left because I have taken 430 pictures of the 500 shots that were still on the camera.

I don't know what is wrong with mil camera. Even when I delete pictures off the camera, it doesn't free up any space. I don't think my pictures are of higher quality so why is this happening. I really don't think that 16 GB can only take 500 shots because I feel like it should be taking 1500 shots. Also, I haven't been taking any videos at all. I have been using the SCN mode a little bit but not that often. If you are confused about what I mean, I can tell you but please any help would be really great. Thanks in advance so much!