It took a few days, but if you ask nicely they'll help you out.
My kid just checked, it's in the right spot now. (He wanted marketplace mods for easier red stone building with more options)
Hello Sven,
We appreciate you for reaching out to Minecraft support. My name is Luke. I will be glad to assist you today. Thank you for the information describing your issue in such great detail.
We will grant a one-time exception and add the purchase of 1720 Minecoins to the correct account. Please note we do not normally do this and will be unable to do so again in the future. Please be very careful when purchasing content or currency and ensure you are logged into the correct account.
Kind Regards,
Minecraft Support,
Luke K.
So yeah it can all be done, it's just general policy not to do it.
