Installing windows 8.1 Pro using OEM key on a fresh build

Hi there, new on these forums and after hours of searching I decided to put up my own thread to get help.
I have a freshly built custom PC and a Win 8.1 Pro OEM key.
I can download the installer using my key and I can download the installer using mediacreationtool.
I can also install those two with the key, but for some reason I cannot activate my windows with it.
It give the errorcode: 0xC004C003
I have tried reinstalling and using the phone activation but it just tells me it has failed and eventually hangs up.
Any ideas on what to do? Getting a bit desperate and considering on purchasing a new license.

Thanks in advance.

Never mind, I called Microsoft Tech help and they determined it being a pirated key and said it will never activate. Money out the window(s) so to speak.