A while back I got a jacket from walmart. Yes, I should have known better. It was ok until a few days ago when the zipper started going bonky. At first it was separated just a little at the bottom. Then it split at about the middle, with the top and bottom both open. I couldn't slide it and had to pry it apart, which opened it but I could not refasten it. Yesterday I tried to fix it and the slider came loose. How do I fix this thing?