Hi @Maximillian31!
Welcome to the Customer Helping Customer Community of Vodafone.
Obviously a very annoying story, what I read now. I don't work at Vodafone, so I can't help you. Understand from your message that you have already been in contact with Vodafone and that you only want to submit your complaint here. I don't know if you have contacted Vodafone via the complaint form? If not, you could try again via this form to see if Vodafone can still do something for you.
The annoying thing is that they will point out the possibility to limit high costs by turning on Blox limited Internet. With BloX Limited Internet you avoid those extra costs. The BloX lowers your internet speed in the Netherlands and the EU so that you have free internet. The Fair Use Policy page states how much data you may use abroad from your databundel. And there is a page with information about using your bundle when you are on vacation. Annoying, but it is clear to Vodafone which countries are connected in order to use Vodafone. Actually, that last page says everything about the use of your mobile within the Netherlands, the EU and outside the EU.
Anyway, I don't work at Vodafone, I'm just trying to explain a bit. Of course it is annoying to have to pay such a high amount. That is why I really refer you to the complaint form to submit a complaint there and clearly explain what the problem is and that you did not incur these costs on purpose. I hope you get a message back from that department with better news. Anyway good luck, I hope you can work it out with Vodafone.
If the text is not clear, apologies. I wrote this with google translate. 🙄