Just shut down those accounts, and if the foreign telecom doesn't comply, then block calls incoming from that telecom. Eventually the scammers will start encountering serious resistance to obtaining new accounts and numbers.
So why hasn't anyone done this yet?
Approximately 50% of the calls I receive are through a company identified as "Sinch". Some complaints about them here: https://scammer.info/t/sinch-and-inteliquent/85531
Sadly, scams are big business.
1) VOIP providers get revenue from the customer (scammer.) 2) Upstream telcos are getting paid by the VOIP provider for the numbers, call origination fees, etc. 3) The receiving telcos get some call termination fees.
No one outside the telecom's accounting department will have the figures handy to know either way. And the net balance would certainly would be proprietary information that won't be shared on HN in any case.
It's not even possible to talk about it in any substantive capacity.