Merci The_Masteres,
...but i was rather lacking some. Well, let's say at this point it's not much to do with luck, except for the part that I was away for 4 days!
Arrived home today with a notification waiting for me instead of the packet. About 12€ VAT.
Now the worst in this story, that previously I had an order from the UK (maybe 2 months ago), and before the package getting delivered I had an e-mail from the post office where they let me pay VAT online with reduced fees. Not this time...
If I was at home, I could've proceeded with the same, until midnight of the date of the first delivery. Now, that was 2 days ago :/

On a side note, I had an order from 2F maybe a month ago, paying the same fees at checking out, and everything was alright. No further taxes.
Fasttech, please spare me now from the "we are sorry for the issues" unless you're willing to reimburse me 12€. Or at the very least the 6$ I paid you at checking out with the order, as obviously, this doesn't work out very well. That makes almost 50%. I'm not kidding. Or that means - again- one customer less for you in the future.
Edited on 11/23/2021 at 5:46 PM. Reason: