What happens to the phone line?

When a telemarketer or company calls me and I say that I don't want their product, they don't say anything then the line doesn't get disconnected, it just goes silent. What happens? For instance, I called a florist a few days ago to order flowers for Mother's Day and when they said they didn't have the product they advertised on their website, I said "thank you though, bye" then the line was still on but nobody was answering. It has happened so many times. What do they do to the phone (because it doesn't disconnect the line automatically)?