Thanks for all your replies!

There is actually an update to the situation, even if the problem isn't solved yet. This morning I had an email from one of two support contacts (according to their website), who told me in a kind of snotty way to contact support by email (!) instead of bothering the sales department.

So what have I done wrong? I think nothing. I went to their website, hit the button that says 'Email Tech Support' and filled out their web form that says 'Contact our support team' and hit the send button. After 24 hours with no reaction from their side I tried to catch someone on ICQ, but my messages are being ignored, even though at least one of the reps was online almost all weekend. Phoning them is no option either because there is still the answering machine that tells me to call during business hours.

So I'm stuck with this poor and unprofessional customer service and have to wait until I get someone on the phone tomorrow.

@David
I'm also on a dedicated server plan with them for over a year now. While their performance is close to perfect with little to no downtime, I've experienced poor and almost unwilling customer services almost from the start. They were happy to help me and do everything possible until I became a customer. But as soon as I had some requests it became difficult.

@Basschick
Yes, they do. But no reply on ICQ (I'm being ignored) and the phone is an answering machine on weekends and after business hours.

@Luke
Thanks for your offer! I will certainly look into options to move to a new hoster next week. I will contact you with requirements when I've talked to my server admin.