Desperately looking for some explanation on how this is all supposed to work though it seems my situation is entirely unique as no one I've spoken to seems to have any clue as to what I should do.

I got Final Fantasy XIV for the 2.0 launch on the PC but started playing on the PS4 when I got one which I found to be much more fun. For that reason I'll be playing Heavensward on the PS4.

I put my 18 digit pre-order code that I got from EB Games Australia into the page on the FF14 website and clicked PS4 and it gave me a 12 digit code saying I need to put it in the PlayStation Store. So I did.

All it did was download some file which I can only imagine is the initial patch being dowloaded...onto my PS4 disk of the original game? I'm not sure how it works.

MY QUESTION IS THIS.
The PS store has nothing to do with my FF14 account, which I initially made for PC. How did putting the code into the PS store add HeavenSward to my FF14 account?
Do I need to put the 12 digit code elsewhere?
Do I need to buy the game for the PC as well even though I have no intention of playing it on PC again?

What am I doing wrong!?

Please help me, anyone. I am desperate to know what on earth I'm supposed to do. I have emailed support but no response. PLEASE.