wish i had read this sooner, i was having the same problem. i downloaded the season pass and didn't get skarlet. tried restarting the game and whatnot and nothing worked. i decided to download skarlet individually, even though it said it would cost 1200 points. i figured it was an obvious glitch and that they would just refund my microsoft points to me after the fact, so i wasn't worried about it. i didn't see any other way of downloading the character.
well it turns out after contacting microsoft customer support, they wouldn't give me my full refund of 1200 points for downloading skarlet, only 800 points since skarlet was offered for 400. i tried arguing with them that i already purchased the season pass for 1200 points, and it didn't come with skarlet, so why am i being charged for buying her when she should have came with the season pass? they were impossible to deal with, and refused to give me a full refund. so yeah, i bought the season pass for 1200 points assuming i would get three characters for the price of four, but they still charged me 400 points for skarlet. so i was charged 1600 microsoft points total.
what was the point of the season pass again? oh right, to get three characters for the price of four. good thing that worked. microsoft wins again.