Welcome to the Magix user to user forums, so not a contact for any Magix staff and confidential data, like your serial number, should never be posted to a public forum, like this one. Hence I have edited your post. Also, no-one who posts here can reactivate that number.
However, I note your serial number begins with "P2" which suggests you have a rather old version of whichever software you are asking about. Which software is it?
You may be able to perform the reactivation yourself, by going to your Magix account, logging in and going to My products. Find the listing for your product and deactivate any installations listed that you no longer use. Then try again to activate your software on your computer.
If you cannot access your account, or you cannot deactivate installations in your account, you will need to email infoservice@magix.net, giving FULL details of your software and serial number, and request their help to reactivate them.