Android system 5.1.1 update error and automatoc appps download, can I get some help?

[chetan08aggarwal]

android system 5.1.1 update error and automatoc appps download

I m getting android 5.1.1 updaet failure. its is 16 mb update and shows notification again again and again after installing the update its shows same update again and now my phone download random apps automaticaaly......each morning i wake up and see new app installed in my device. igave my cell to service center they remove the problem and now next day when update notification again come and same thing happen again.
i dont kow what to do plz help me ourt here ....is there any provision to replace my cell?