Motorola Moto G — Caller ID

The caller should had made an anonymous call to you.

Chumphr

Thanks but it happens on every call. I've even tried calling myself from my landline and the phone still displays "Unknown Caller".

If it happens on every incoming call, you had better contact your carrier to check whether it provides a caller name delivery service known as CNAM for your SIM card.

Have you checked if the contacts have included the country code before their phone numbers in your phonebook?

Which phone model are you using?

To fix the issue of calls showing as "unknown number" even for contacts, try resetting the phone's network settings or contacting your service provider for assistance.