...
These are the sites where you should submit the request for the number to not be treated as SPAM.
T-Mobile
https://callreporting.t-mobile.com/
Verizon
https://voicespamfeedback.com/vsf/
AT&T
https://hiyahelp.zendesk.com/hc/en-us/requests/new?ticket_form_id=824667
You can also try going to this website and registering the phone number, so it is no longer tagged as spam.
Please note, that this is not a Sangoma-related website.
https://www.freecallerregistry.com/fcr/