I had my first one ever earlier this week.
Woman with a south asian accent claiming to be from BT internet.
She asked how my internet was today, I replied I didn't know (true, I hadn't used it at that point).
She then told me that there was a problem, and I had to turn on my computer, I said it wasn't convenient (not entirely true).
When I asked her who my service provider was, she was unable to tell me, but said it didn't matter, all providers were affected.
At that point she said that I'd be cut off within 15 minutes, so I said I'd take it up with my service provider, and she rang off.
Several days later, I'm still in online.
Adrian