We are sorry you were charged more for your purchase. Unfortunately, we do not have any control over a customer being charged any extra fees, such as VAT (value added tax, common in the EU) via Steam, from currency conversions, or other fees the payment processor (Steam, Google Play, Apple) may have charged you depending on what payment method you chose or your location.
You are welcome to go to the Help Pages/Support for Steam, Google Play or Apple directly for more information. Here is our Payment Help Section for General Artix Help that includes more information about the payment processors we use to purchase Artix Points.