Question
Why am I getting angry calls from people who say they received a call from my Twilio phone number?
Product
Programmable Voice
Answer
If you don't see those reported calls in your Twilio call logs, it's likely that you are a victim of an issue called 'caller ID spoofing'. Caller ID spoofing is basically some bad actor using your Twilio phone number as the caller ID on their outbound calls without your permission.
The FCC defines call spoofing as follows:
Spoofing is when a caller deliberately falsifies the information transmitted to your caller ID display to disguise their identity. Scammers often use neighbor spoofing so it appears that an incoming call is coming from a local number, or spoof a number from a company or a government agency that you may already know and trust. If you answer, they use scam scripts to try to steal your money or valuable personal information, which can be used in fraudulent activity.
Additional Information
Options are limited, but the best course of action if you are in contact with the call recipients is to encourage them to report the behavior to their carriers. The call recipients' carriers have mechanisms to trace calls back upstream in some cases (especially when they are willing to take legal or law enforcement action), whereas Twilio does not have that ability since Twilio was not in the call path for these calls.
The FCC has the following recommendations from the Q&A section of their caller ID spoofing page:
If you get calls from people saying your number is showing up on their caller ID, it's likely that your number has been spoofed. We suggest first that you do not answer any calls from unknown numbers, but if you do, explain that your telephone number is being spoofed and that you did not actually make any calls. You can also place a message on your voicemail letting callers know that your number is being spoofed. Usually, scammers switch numbers frequently. It is likely that within hours they will no longer be using your number."
Additionally, the FCC recommends that if you think you've been the victim of a spoofing scam, then file a complaint with the FCC.