I redownloaded the game again on Steam.
No issues there, connected my Battle.net account and started it.
I checked out the shop and wanted to buy the Invasion Ultimate Bundle.
Clicked it and got redirected to Steam, where I purchased it.
The problem is now, that the game itself doesn’t seem to notice that I did so, since none of my items show up in game.
Obviously I didn’t want to pay 40 Euro for nothing, so I tried to refund it, which of course isn’t possible for this DLC.
The Steam support page says I have to get in touch with Blizzard directly, that’s why I’m here now.
Please advice for what I should do now to resolve this issue.
Best regards