Santin X3 Memory Issue ,Google Play store error, Constant App & Process Crashing

A few days ago I bought a Santin X3 from DHgate. Everything was great but after a little while I couldn't download any app from Google Play Store it would either say a"Packge File is Invalid" or Error 492, also when I try installing any APK it says "Package is corrupt" or "insufficient space" and that's where the memory issue comes, when I go to Settings>Apps it says "6.3 GB used and 9.5 GB free" Everything that I have downloaded doesn't even add up to 6.3 GB and I have lot of free space. Also When I go to the Running Tab the RAM is always Stuck on 0.92 GB out of 1.0 GB no matter what I do. I have one more Problem most of the Google apps and Facebook keeps Crashing and this one process called com.google.process.gapps keeps crashing. I know I have about 3-4 Problems but I would like some help. Thanks