Please follow the instructions below in order to solve this issue.
- Uninstall Truecaller.
- Upgrade to iOS 10.1.1 or higher.
- Install and setup Truecaller account.
- Restart phone and try again.
If you're using iOS 10.3 (BETA) please make sure to upgrade to latest version.
If the issue persists please contact us at "Support@truecaller.com"