I've never heard of Truecaller, and would never use it. I do NOT expose my contact list to anything or anyone out of respect for the vulnerability of that data, the contacts themselves, and the possibility of its misuse. I would never trust any 3rd party security keeping that data safe on their systems.
Asking questions is a skill CodeProject Forum Guidelines Google: C# How to debug code Seriously, go read these articles.
Dave Kreskowiak