I understand how these call would cost Instagram/Google/Microsoft money. But, could someone please explain why a call to a premium number "earns" the account holder money?
So what he did was to get one of those numbers and then have Google / Facebook / Instagram call that number repeatedly and that's how he would get money.
The cases of telecom fraud that I know of that were caught are usually due to incredible arrogance on the perpetrator's fault. In one case, he actually called the company he was attacking to gloat that they could never get him. (The company used a super-vulnerable-yet-expensive switch that literally had bugs like "&admin=1 gets superuser".) I've not seen a VoIP system that was remotely secure.