What is the dabba calling extortion technique being used by gangsters?

Gangsters like Goldy Brar, Anmol Bishnoi and Rohit Godara are using dabba calling extortion method to issue threats to victims in India. This technique involves a henchman placing an online call to the victim and using a second phone (dabba) to call his boss in a foreign country, keeping the phone side-by-side and letting him issue threats to the victim.