This is a standard, and terrible, practice with many large companies. They want you to call them so a "customer retention" specialist can try to talk you into not cancelling. They'll usually offer you a great deal to stay.
On the flip side, this process can be abused by people who don't actually intend on leaving to get better rates/prices. I've done it a few times over the years to deal with rising costs of an ISP when I don't have any good competitor to actually switch to.