Since the recent changes, you can’t anymore gift balance that you already have to friends from the same country. For example, in my balance I have ARS245 and I want to gift ARS245 to a friend. In order to do that, I should purchase ARS245. I can’t bift balance that I already have anymore. One week ago I could gift someone balance that I already have, now I can’t.
Also, the international credit cards are now declined. I’m from Argentina, but because of the pandemic I’m in another country and I can’t buy anymore anything in my currency.
That is intentional. That is how Blizzard Bnet balance gifting has worked for a long time in the US. If it did not already work that way in Argentina then that was a mistake. To gift you are supposed to buy new Bnet Balance and gift it at the time of purchase.
Please read the support article on it - it notes you can’t gift Bnet Balance you already have.
This is also intentional.
The currency of your Balance must be the same as the currency displayed on the Shop. For example, if you added Dollars and you visit the European Shop, you won’t be able to use your Balance because the European Shop charges in Euro.
The currency that Bnet accepts is based on your Country of Residence for your Bnet account - as in where you live.
You know all this though because you already talked to Support about it and you posted your results on the WoW forums.
You don’t live in Argentina so you don’t pay the prices that people who live in Argentina pay.