I'm afraid you did it backwards. The offer from Bungie is a digital upgrade path from the 360 to the One - not the other way around.
I play on both consoles and just bought the dlc for the Expansion Pass for the 360. I then got the dlc for free for the One.
English
-
I ran into this problem as well...I called microsoft and got them to refund me the purchase on my xbox one so I could repurchase on the 360. Took 15 minutes. I'm relieved.
-
Darn it! I did the same and now that's a bummer....why not the other way as well ?
-
Because it is an upgrade path - not a downgrade. The promotion is to spur on the sales of the new consoles.