Is app breaking app developer rules?

There is a language app called hellotalk, available for both android and iPhone. On both versions I have heard similar complaints.

hellotalk seems to be able to identify you exactly. I’m not a tech guy so I don’t understand how they r doing it but seems like a privacy issue.

If you are banned from the app you can no longer enter the app. You cannot create another account using another email address or phone number etc. indicating to me they know exactly your unique phone Id. On android apparently the app doesn’t even open. How r they able to do that?

isn’t this a privacy violation from the developer? If so how can I report them?