Rekordbox DJ License Key Deactivation Problem

So here's what I have done I installed Rekordbox DJ on my laptop I then upgrade my laptop's hardrive formatting the drive before selling it I did not deactivate Rekordbox DJ before formatting the drive I then installed new hard drive and installed Rekordbox DJ I have since sold my ddj RR and deactivated Rekordbox DJ on my laptop, I have given the buyer the controller and the Rekordbox DJ Software but when he enters the key on his laptop it say Rekordbox DJ is being used by someonelse how do I go about resolving this or how does the buyer resolve this as have formatted drive and sold on thanks any help would be really appreciated

Best regards
Pete