My heat turns on while the car is off and drains my battery! How can I fix it? on 1999 Cadillac DeVille

The problem is constant. I need this fixed. I have no clue what causes this and I need help. Please tell me if you have the same problem and what caused it! Help is appreciated!

Asked by for the 1999 Cadillac DeVille
Are you referring to the blower is running.