A Blizzard customer support employee advises players in that situation to get in touch via the game key problem option of customer support.
Warlords of Draenor is now part of the base World of Warcraft [official site] game, meaning it’s included when you buy WoW so no need to pay extra for the expansion.
This basically brings your account up to date with WoW’s story so far/current state in preparation for the upcoming sixth expansion, Legion.
There’s not an enormous gnashing of teeth or anything, it just seems like the switchover has been lacking a little in clarity.