Had that problem myself last year...it was a technical issue with the Magix dns entry. Got this instruction from support and it worked:
Hi Howard,Regarding your serial: Please send an email with your order number to infoservice@magix.net. Then my colleagues can verify that you took the VEGAS Pro 16 + 17 deal. Either they will send the serial to you or I will through this chat.The technical issue you mentioned is forwarded to the responsible person. I hope you understand that I can't give you insight if your suggestion will implemented.Best regards, Mathias