We were with BT broadband. I cancelled and moved to sky. I then received call after call telling me to come back to BT, that they would pay off my sky contact. They implied I was stupid because I couldn't understand how much better they were than sky.
One of the reasons I left was because whenever we had a problem it seemed impossible to get BT to send an engineer. I was sick of crawling around on the floor taking sockets apart and god knows what else before they eventually accepted that they needed to send someone out.
The calls eventually stopped when I told them to stop calling or I would report them for harassment.