How do data brokers get a list of all the phone numbers on my cell phone account?

Web: https://www.reddit.com/r/privacy/comments/vleqhf/how_do_data_brokers_get_a_list_of_all_the_phone/

I keep deleting entries that include my family plan phone numbers. Does the cell phone provider sell that info directly? It's the only thing that makes sense. those numbers are only associated with me through my mobile cell provider.

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