Not sure if this is posted in the correct area but please bear with me.

I recently emailed Garritan to ask for permission to sell my copy of GPO.
Permission was granted so I contacted Native Instruments to let them know. They responded and gave me a new serial number to give to the new owner.

My GPO has now been sold but the serial number I gave to the new owner does not work. It says 'Serial Number already in use for another user.'

I have contacted Native Instruments four times now to try and get this sorted out but I have been completely ignored by them. I would be tempted to phone them but unfortunately I cant speak German.

Does anyone have any advice on how to proceed from here?

Thanks - Mark