There is no phone number to contact Magix! Like a large number of companies today, support is either via user to user forums like this one, or via a Support ticket system. Assuming you have a Magix Account this page should help you.
But, why not give full details in a forum post about the problem you have, ensuring you select the correct product area and include full details of your computer? Should you actually have a problem with a product from the Magix Vegas range, please see this post.