Do not DIY this. If the number you're flooding terminates in the US, you can be subject to big fines.
Miami man made 96 million robocalls to sell vacations packages and faces a $120 million fine from federal regulators
It
probably terminates in another country, but you have no way of knowing for sure. If this method shown in the video were to become popular, as a countermeasure, the scammers could simply redirect where the flooding calls go and send them to the US instead. Then they could document the flooding to their US call center, have the Feds track you down and you would get fined.