How to top up credit on a Vodafone

Hi,
At the risk of sounding like a complete idiot, I've a new phone, a voucher from Rossmann to top it up, and no idea how to do this. My German is limited to say the least! Is there a simple process ie. automated number to call, tap in the code and ta-da? No mobile shops anywhere near me...I'm trying to translate the info that came with the phone, but I've now been doing this for days with no success.

There's a way to make your phone talk to you in English - either look it up in the instructions or take it into the shop and stare pitifully at the person behind the counter.

Kontoserver should be one of your preprogrammed numbers; call that to top up, but I think you have to go through a couple of menu options first.