@Edent I work at a call center and one of my coworkers recently had a similar exchange with a scammer like this targeting someone in the US. They were speaking with someone who was giving noticeably delayed responses to questions, and got suspicious since there was a history of this customer being a victim of fraud.

Turns out it was this exact scenario - one scammer in a pair on the phone with the customer, the other on the phone with us. My coworker thought something was up, so he put the caller on hold and did an outbound call of his own on his second line to the phone number we have on file. Sure enough, someone else - the customer's son - answers the phone, and confirms that the customer is on the phone with someone claiming to be us.