Rekordbox Key - DDJ-RR

Hi,

Im running Rekordbox V5 (my computer operating system won't allow me to upgrade to V6), and I bought my DDJ-RR second hand and the license key that came with it says it is being used by 2 other computers and hasn't been de-activated. I won't be able to get the former owner to de-activate it and thus purchased one of the monthly subscriptions, however, have realised these are for version 6 and not 5. How do i purchase the monthly subscription for v5 so I can access the performance mode and use my unit?