tl;dr This summarizes it perfectly.

  My phone call [to a disconnected number] never actually made it to Cuba. The fraudsters make money because the last carrier simply pretends that it connected to Cuba when it actually connected me to the audiobook recording. So it charges Cuban rates to the previous carrier, which charges the preceding carrier, which charges the preceding carrier, and the costs flow upstream to my telecom carrier. The fraudsters siphoning money from the telecommunications system could be anywhere in the world.