You cannot. DirectTV, if like Comcast, AOL, or Dish, simply WILL NOT let you cancel...which is why I won’t do business with them in the first place.
...a bit of an exaggeration, but not much. Good luck!
They can be pretty ornery when you try to cancel or downgrade; they keep trying to pass you off to better ‘closers’. You just have to keep politely saying ‘no, I want to cancel, please’, and wear them out :-)
Be ready to spend quite a while on the ‘phone; but when it’s done you’ll feel triumphant!
-JT