Go to https://www.magix.com/gb/support/my-service-center/ and log in with your account with your email address (the one you registered with) and password. Then go to My Products and you should see your purchase of Vegas Pro 16. There is a download link that will allow you to download your software. There will also be your serial number shown. Make a note of this as you'll need it after you've installed the software.
Thank you for your responses. I have used the Vegas 16 Pro since March however it doesn't show up in my registered products let alone being able to download it. I can't seem to find a customer service phone number that works.