why is my lumia 550 adding contacts by itself and deleting my call log and messeges by itself

[falem]

my lumia 550 is adding contacts that i dont know and deleting my call logs and messeges. i get random messeges from people i dont know. it saves contacts i dont know as 'retail demo contacts'

 

[Ryujingt3]

When do these contacts get added? By that I mean what are you doing on the phone at the same time that one of these contacts is created? Can you give us more information?