Enhanced Level 70 Character Boost

I purchased the enhanced boost, can see it on the character load screen, but am unable to use it. I have a level 60 character boost (given when subscribing to another year of WoW) and a level 70 character boost recently purchased. When selecting either of them, it does not allow me to select existing characters. It only allows me to create a new character. I have a level 50 Dwarf Hunter and a level 50 Tauren Druid that could both benefit from the 2 boosts on my account. Neither are able to access the boost or be chosen when selecting the boost from the lobby menu.