As someone who types in anagrams, I can assure you that it's an easy mistake to make. You write a letter to Santa, and a simple transposition of letters means it goes to Satan instead. The filmmakers at Anomaly London went with it and speculated on what Satan would do when he got one of those letters. This story is not for children.
Hope constructed her letter well, beginning with admiration for the recipient. That threw him off-kilter immediately. Even Satan can be vulnerable to the power of love. Enjoy this peculiar vision of hell, with an ending that will make you laugh and then feel guilty about it. -via Tastefully Offensive