Windows server 2008 R2 180 days activation in Virtualbox

I have a testing machine that needs Windows server 2008 R2 running in virtualbox. My issue is that every time I try to activate windows I get the error "security error 0x80072F8F"
I set the clock according to internet time
I called MS and they said WS2008 is no longer supported I tryied also with dialup activation but it says no answer, the modem itself works and also the POTS line. I must say that some other WS2008R2 VMs have been activated.

Right now I tried to:
• make a new VM with my existing iso
• download an iso and make a new VM
• Update Virtualbox and make a newer VM

In no case I was able to successfully validate the 180 days trial licence

How could I activate the 180 days trial licence on a Virtualbox VM?

NOTE: I'm not going to purchase a new licence because this machines are needed just for few months and just for testing.

EDIT: Setting HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\OOBE for an item named MediaBootInstall to 0 did not worked

EDIT2: slmgr /rearm: this gave me other 10 days grace period, but it's still impossible to get the whole 180 days (the bottom right of the desktop does not shows "180 days left")

The error x80072F8F when attempting to activate Windows is caused by the time on your system not matching the time on the Microsoft activation server, thus it blocks your access.

Fix the clock on the virtual machine to be correct within its declared time-zone and it should work.

If that didn't help, check registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\OOBE for an item named MediaBootInstall. If it exists then its value must be zero (0).

Another try is to run Command Prompt As Administrator and execute the command slmgr /rearm and reboot. If asked for your product key, then type it to activate Windows.