Why are unknown contacts getting added in my phonebook?

Hi Guys,

I have Sony Xperia M device with android 4.3 (Jelly bean).

Contacts in my phonebook are automatically increasing without any notification. Whenever I check my phonebook I see new contacts are getting added automatically and the size of contacts is increasing day by day.

I checked my auto sync option in settings and it is already in disable status.

So how can I stop downloading these contacts.