How can I order Internet for a flat in Belgium as a German citizen?

For our flat in Belgium we would like to order an Internet access. The flat didn't have internet before, so there is no "easy switch". During the ordering process I have to enter my details including numbers from a Belgian passport- which I do not have, I am German. I could identify myself via ItsMe, but when I do that the ordering process does not advance, as a Hey account with the same mail address as in ItsMe is required first. I can't create a Hey Account first though, as this would require a GSM number or an "Easy switch ID".

So - I am stuck, plus I can't call, as the 0800 number is not reachable from our German phone network. The Hey service can't call me as well, as they can only call Belgian numbers. 

Does anybody have an idea, how to get an account created, if I cannot do it in any way myself? I just would like to order a new internet access...

Is there maybe an email address where I can send my details to? The service chat cannot help me (also real persons in the chat).