Hallo Susanne, herzlich willkommen im Forum!
Receiving different order numbers is fine, as these are different orders. As noted by @heikkiap above, you should have used your personal “discount code”/pre-payment voucher in the check-out. The old order number is not needed when you finalize your order for the phone.
You can’t and you don’t need to, since you have already ordered everything you want.
Edit: Below you wrote that you have in fact used the code, so all is good.
However, when I read between the lines, I get the impression that you didn’t apply the “discount code” and so paid too much for the phone. Please see the FAQ on how to proceed.
I’m sorry that you got that impression, as you would in fact have found answers there.
Please instead check the FAQ.
MfG Erik
PS
Thank you for taking the effort to writing in English, which is the preferred language in this forum.
If you wish to discuss in German, you should use this thread: Talk about SailfishOS in German 2 - Unterhalte dich über SailfishOS auf Deutsch
However, you need to be aware that this is a mixture of many topics and may be hard to follow at times. Also, sticking with English helps more people here, as that is the language most of us are familiar with.