BTW, Its the same with most of the free app one downloads. We accept their usage conditions without even reading a word. Depending of what you accept, you give access to everything. Imagine, you give access to your phone camera, microphone, messages (email/sms), application usage stats, etc. So they use all that for their advertisement, marketing and other benefits.

Now regarding the truecaller... by just deactivating your account, you get safer only for the new contacts going forward, but what you have already given to them is already theirs!

Be very careful about what app you download/click/agree, ensure you read and understand before you give permission.

Everything is recorded! Its a scary world now!