Darn you Games Workshop!

So it was my birthday and my cousine wanted to surprise me with two Games Workshop online vouchers. One for 20€ and one for 10€ because a 30€ voucher doesn't exist.
Five days later the vouchers hadn't arrived yet and so she had to call the mailorder. They excused themselves and sent the voucher codes to her and she forwarded them to me. So I activated the codes and was happy for now.
Few days later I wanted to use them and choose some stuff into my shopping cart for about 30€. As I wanted to choose the vouchers for payment I found out that you are only able to choose one voucher per order. What the Hell?!
So I cancelt the order with quite an angry mood.
A day later I decided to order though I am only able to use one voucher (still: what the hell?!). I placed the Krash Thrax from the Inquisitor range into my shopping cart and went to payment. I properly entered my bank account for the remaining 5€ and entered the code for the 20€ voucher. The page sowed me that I had still 5€ to pay which was surprisingly correct. As I clicked the button for sending the order the page started to load and load. After that was done the page showed me my bill and the details to my order that said "amount to pay: 25€"
I shortly was confused and shocked. So I checked again and thought "Maybe the voucher is just not shown" but as a I went back to "My Games Workshop" there was still the 20€ voucher listed as available.
I got a "crew stunned" result...
So I grabbed the phone and called the mailorder. The guy there told me that I might have made a mistake... I told him insistend that I followed all points correctly.
I had two options: First was to cancel the order what was only possible if the article hasn't already been packed or second, I let it be and pay the 25€.
I choose to cancel the order if still possible. He told me that he checks that with the department and give me an email how it turned out.
That was last Thursday, that's 7 days ago and I'm still waiting on that email.
By the way: the money is already gone from my bank account and the model hasn't arrived yet.
Thank you Games Workshop!