I remember one time when I was really bored, I got a scam call and it was clear as day:
I always reply in english (I'm spanish) so whoever was at the phone got confused and said "wait a second please" very poorly. Then I got someone speaking perfect english to me, saying hello sir I'm bla bla and I replied in spanish "I don't understand" so he said to wait a second again and got someone else to speak in spanish the same lines. So I did the best thing I could, reply in german since I'm a man of languages - he got extremely confused and said to wait, eventually someone with a super broken german came in and tried to do the scam thing. Seeing this cycle and that it was working, with all my boredom all I could reply was "¿Qué?".
And thus I made them spend half an hour on me until they were the ones that gave up.