[2021] DLC completely gone from my account.

The only way anything gets removed from a Steam library is if Steam remove it. You don't seem to have bought that DLC from us, did you get it from Steam directly or some third party?

If from Steam directly it will be in your purchase records there, if so you can contact their account support and ask why it was removed.

If it was from some third party, who was that exactly please?  

G2A are a grey market vendor who resell keys that can be stolen or bought with fraudulent credit cards. We got none of your purchase money, which is why they are so cheap.

Almost certainly Steam have detected that and revoked those keys.

Please only buy from our store, Steam, or one of our authorised resellers:

Approved re-sellers

Hello everyone. I've been wondering for some time, who/what actually are the "approved re-sellers" that Paradox considers legitimate? Is there a list Paradox has made, which has all of them? If not, why? I'd think something like that would be... forum.paradoxplaza.com
Sorry that happened to you!