I tried to do the upgrade five different times and every time I try to go to the payment screen it says I have nothing in my cart and wants to take me back to other unrelated products. This offer ends tomorrow so I'd like some answers.
No, sorry, all support is via this (user to user) forum or by creating a Support Ticket. Or you could email infoservice@magix.net and ask them, though clearly you should not expect any reply before Monday or Tuesday at the earliest. But I think there is no harm at all in pointing out in the email what you are experiencing and asking them to allow you to purchase at the special price.
HTH
Jeff Forum Moderator
EDIT, to add: another user has reported a similar issue in this thread (in French) so it seems this may be a website issue.