C&C3: Tiberum Wars can't login during game startup

Hello! Just purchased C&C3: Tiberum Wars (only that game), downloaded and installed it through Origin.

Can't run it, thought. And I'm not talking about Windows 10  (am running win10 x64) or whatnot compatibility issues, I'm talking about that forced registration popup you get when first starting the game. The green startup picture appears, and a small dialog box above it asking for my e-mail and password. I suppose it needs to be my Origin (formerly EA) account e-mail and password. I enter it, and click the button, but some red text appears below and won't budge further.

I'm saying "some red text" because the dialog box is in Czech language, which I don't understand (all my localisation settings are set to ENG, so - no idea why that is).

Whatever the case, I simply can't login, and thus start the game.

I've tried the following:

1) Set compatibility mode to xp sp3, win7 sp1, run as administrator both C&C3.exe and Origin itself

2) Disable UAC

3) Uninstall my antivirus and totally disable windows defender.

4) Uninstall Origin and game, and install it to C:\ drive

5) Create a pogo accout, add that persona to my origin accout

6) Tried to use my password from pogo

7) Restart my computer and origin multiple times

8) Searched what seems the whole internet for an answer

All other Origin games (and games in general) work flawlessly.

What gives?

I'm this close to asking for a refund. And by the looks of it, I'll do it.