When we place order, first we make payment, if by Paypal we get confirmation from Paypal, or any other third party in case of Credit card.
Then we get confirmation e-mail with subject line "Confirmation of your order from Magix" alongwith Order Number, Serial Number and download links.
Did you purchase from Magix or other place?
So, as you are saying you did not get serial number did you check Spam folder?
some times mail land in spam folder.