Why is my number showing as SPAM?

This issue usually happens on the receiving end’s carrier. It is due to some spam controls on the carriers that marked this number as Spam. The DID is probably being spoofed by spammers/scammers that other providers are seeing your customer’s number as SPAM already. Unfortunately, there is no way to identify spoofed numbers because they come along the same path and look the same as a legitimate phone call. You can report these calls to the FCC for further investigation. Below are some helpful links on Spoofing:

https://www.fcc.gov/consumers/guides/spoofing-and-caller-id

Below are links to sites that will allow you to Whitelist your telephone number.

AT&T

https://hiyahelp.zendesk.com/hc/en-us/requests/new?ticket_form_id=824667

T-Mobile

https://calltransparency.com/

Verizon

https://voicespamfeedback.com/vsf/