If you pre-purchased Heart of Thorns from third parties, they are likely fraudulent.
Heart of Thorns is currently only available officially to purchase through our purchase site and in-game through the gem store. There have been a number of 3rd Party websites/services offering Heart of Thorns for sale, and none of them are currently officially authorized to do so.
These sites are most likely getting their keys through fraudulent practices, which means there is a VERY high chance that if you purchase from these websites that the key will be disabled shortly after. This will result in your account being closed for fraud, and Customer Service will require that you purchase HoT though legitimate means before you can access your account again.
For your account’s sake, please be careful when purchasing your HoT key through a 3rd party (right now).