So, what do the con men do? Make my internet even slower?!?

I've had similar upgrade calls before without problems. The ISPs mainly check that my mobile phone and internet subscriptions are up to date (and possibly sell me something extra on the side) so that I don't say phuck it and run to their competitor.

Identity theft. Do I need to list what they can do with that?

He didn't ask for my ID number, if that is what you are suggesting. Yeah, if someone asks for it, I'd definitely ask where does he/she need it. I'm not giving it to anyone for free, 100€ a pop.

Anyway, he was quite convincing. He knew what phone numbers I have, how fast my internet is, and what were my last monthly fees for them.

I was in a good mood and distracted and not cynical and suspicious enough. I want to think people are good unless proven opposite but one should always suspect the worst of people.

Hmm, now I am starting to wonder what are you trying to achieve with all this...? What is your hidden agenda?