Regional Pricing - Support Pack Upgrage in game

Hi,I bought the game on Steam. I got the game price according to my country through Regional Pricing, but when I want to upgrade, the in-game pricing is not Regional, so when I want to upgrade the supporter pack, I have to pay the full game price again. Can you help me find a solution for this? I don't have the option to refund the game, after all, I played for 11 hours.