Steps to mitigate a phone number that has been spoofed / hijacked by someone else:
1.Check the skype call logs to make sure the client is not actually making spam calls.
Through Partner Center access the Office365 admin center for the client tenant.
Click on the Teams / Skype Admin
Click on the Legacy portal with Skype icon next to it
On Left click on Reports – This will bring up the PSTN logs
2. If the logs do not show an excessive amount of outbound calls inform the client that their number may have been spoof / hijacked.
3. Help the client file a complaint with the FCC:
4. Recommend redirect all calls to voicemail
5. Create a voicemail message that states something like:
“My number has been spoofed. I did not contact you. Please block my number.”
If it is a business number you may wish to proceed the above line with:
“If you have called for <Company Name> please leave a message…”
6. To cover the mobile side recommend that they get one of the many call blocking apps which can be searched for with “spam call blocker”. Essentially it only allows calls from your contact list to come thorough, all others directed to voicemail.
At this time there is no other way other than changing the number or riding out the storm