I bought a 10er Premium lootpack for 9.99 euro for fortnite battle royale 1 hour ago but didn't receive it. I have already done a lot but still haven't
If you bought this through an external app that doesn't work for or for fortnite. I would advise against it soon.
Otherwise I would write to the developers of this app and ask for the goods. What I often do is film the purchase or take photos as proof.
I don't know how old you are, but if you can also ask your parents for advice.
I wish you much success in solving your problem.