These are user to user forums, not a contact for any Magix staff, sorry. And you should never post your email address, or other personal confidential data to a public forum like this one. Hence I have removed it from your post.
Magix Cancellation policy is detailed here. In the meantime you need to contact infoservice@magix.net with full details of both purchases and ask that they cancel one and refund the money. Just be sure to say which emailed serial key is no longer to be used, or you may find that the app no longer functions because the "wrong" serial key has been deactivated.
One final thing: these are NOT the forums for Magix Vegas products. Please read this pinned post, so this thread will be closed.