Dear God No.
An exclamation used to express your utter repudiation of a person, place, thing, or idea. You are insinuating that if you could send a letter to God, the contents would entirely be "No".
Example:
To: Heaven, 777
From: Somewhere in North America, 12345
Dear God No.
Not So Sincerely,
Sender
To: Heaven, 777
From: Somewhere in North America, 12345
Dear God No.
Not So Sincerely,
Sender