It's entirely normal your key for MSFS won't work in P3D, since they are two separate products, each one with its own separate license.
As with anything related to orders, you should contact support by email, something I see you already done so, there wasn't any need to repeat this on the forum, the obvious reason why you haven't been replied YET, it's because you emailed during the weekend, on new's year day too but, of course, you WILL be replied to, during normal working hours.
