You could do what I did - cancel, than call back 3 months later screaming that they don't offer existing customer promotions...
They are at least willing to bend a little in that circumstance - or if your monthly bill is large enough you can threaten to cancel by calling them, they'll transfer you to a retention csr who will offer you at least one month free - explain to them why you are leaving, tell them you'll pony up the $399 if they'll give you two months free. If your monthly bill is $50-$60 it will be like getting $100-$120 off the receiver price...
Chris