Win not activated?

This is why you should always double check the key by clicking the store page from the giveaway page to make sure that steam says "You own this product" or whatever it says. I have seen mistakes of people clicking the wrong product that share identical (or near-identical) names.

But beta/playtests keys are not allowed to be given away according to the guidelines so this giveaway should be deleted - https://www.steamgifts.com/about/guidelines

Mark the giveaway as "Not received" since you didn't get the game the giveaway was for.

You can also leave a comment within the giveaway that you got a key for the wrong game and ask the giveaway creator to replace the key with a key for the correct game (Beta versions of games are not allowed to be given away).
If the giveaway creator refuses to do so, a solution can be to have the giveaway deleted. For this to happen, you have to write in the giveaway itself that you agree to a giveaway deletion.

But you don't have to do all these things, in theory it is enough to just mark the giveaway as "Not received" and move on.

I had a similar problem. I marked received without verification. I had to contact support. They asked me to make a couple of screenshots to confirm my words. The problem was solved and advised to be more careful
Sorry for my english, i use autotranslator

Some games which are full say beta or testing when activated - nothing wrong here

edit: you shouldn't of marked it not received when you DID receive it also how long since you tried to contact them did you leave it for them to reply?

You got the full game I couldn't even find a play-test version on Steam - you only contacted him 4 hours ago and you can clearly see they were only on last 7 hours ago - so they haven't even seen your comment

Sorry to have a go but I think you have been a bit unfair to them here

In another thread I saw someone mentioning that sometimes after activating a game it gets marked as private by default. Maybe it's something like that?