> Scammers hijack the call

How do you do this bit? Is the caller deliberately cooperating, or they think they're using a real service?

I remember calling transcontinentally in the noughties - I would top up an international calls account. If I recall, I had bought a card from a shop with a scratch-off panel. To call first call a local number, then enter my account number. I would pay local rates for the call which were bundled with the contract, so free on the margin, and the call would cost me some pennies per minute from my calls account.

I have no idea how they completed the call, but I was thrilled as it was just before the time when you could just use apps, and the calls would have been ruinous otherwise. For all I know the whole network was a scam. Things like phone cards, money remittance etc, all seem pretty scammy anyway at the best of times.

Yes that's what popped in my mind too. Calling from abroad to back home, I would pay for a card. I would call the number on the card, the code, then my destination number then the hash key or something. I don't think I topped up it.

I imagine this could work the same way.