SAMSUNG S4,ANDROID LOLIPOP 5.1,2GB RAM, 16GB STORAGE AT IN INDIA

The phone have 2GB ram and 16GB storage, it was excellent till 22nd while running android lolipop5.1, i gave a mobile shop to install android marshmallow update, somewht happened now front camera and wifi automaticaly turns off in two three seconds, the technician says it has to be installed freshly to make it work and the driver for tht may got corrupted software, but i lost all my datas and numbers stored in mobile, i am verymuch disappointed to use it further, if any of them have idea to buy pls let me know, its negotiable a little but dont bargain below an average coz i hate bargaining guys, dealers pls stay away, jst text me b4 u call, dnt blame me if i get rude aftr tht. looking for decent and genuine buyers, mobile is working fine other than that