If you have bought the game and not received the discount please contact Valve. here:
https://help.steampowered.com/en/wizard/HelpCompletePackagePurchase?appid=1016790
This discount (as long as you played the open beta) is guaranteed - so please know that it will be honoured.
We are in contact with Valve right now to get this issue rectified and it will be sorted as soon as possible. This discount is applied in the Valve end of things so there is little we can do from a dev side, but please know, the discount will be honoured and we are doing all we can.
We apologise for the inconvenience.