Keeps calling my minor child's private phone. Despite me answering and telling them to stop calling and harassing my child, they will not remove the number from their call list. They keep calling, which is a form of harassment and stalking.
Since you've answered and spoken to "them", you're the first in this thread in a position to honor the above instruction to "help identify who is using this phone number". Once details are known, such as the type of caller and location, it will be simpler for all to decide how to handle the intrusions.