If I remember correctly, when I cancelled my account one of the conditions was that the account needed zero activity during a long time before being deleted (one or two months if I remember correctly)
Here comes the trick: This means zero activity from your part on everything you had in your account. Meaning that any app or webpage that you authorised/registered with your facebook account must be disconnected before asking for closing down.
If any app or any webpage posts/makes any automatic activity in your account, like posting an advertisement or an automatic reply, that counts and cancels the deleting.
Therefore: cancel any third part access to your FB account, and then disconnect all your browsers from automatic access and delete the mobile app. Zero activity means that: nothing. Not even a login.
Then it will work. Or it should. They are so desperate for users that who knows if they will comply. One thing to keep in mind is that they will keep all your data for years. They won’t delete it right away. At least you will not keep them updated…