This seems to be the third thread you have created about this problem! Please do not create duplicate posts. One of the others has already been closed, I will close the third.
Where, exactly, did you purchase the app? It would seem you now have a second-hand/second-user copy. Is that correct? If so, you should either, ask the seller (assuming he/she was the previously-registered owner) to inform Magix (email infoservice@magix.net) that he/she no longer owns this software so the current registration details should be removed from his account. Thus, when you attempt to register the app you should be able to do so without problem; or, you should immediately ask the seller for a full refund of the purchase price and then go to the Magix website and purchase the latest version.
To directly answer your question: no-one, including Magix staff, can, or will, send you a NEW serial number. Whoever sold you the app is solely responsible for arranging the transfer of ownership.