Which product, bought from where? (I assume direct from Magix.)
These are user to user forums NOT a contact for Magix Support. Assuming you bought whichever product you have direct from Magix, any invoice would have been delivered by email, so have you checked all your recent emails.
If you definitely have nothing in your email Inbox you will need to contact Magix Sales by using the Support button in the header of any forum page. No-one who posts here can help you with this problem.