contact steinberg support.
http://www.asknet.com/company/customer-support.html
Beware, since it is a holiday period so it may take some time.
You can ask for changing to the correct upgrade or ask for a refund.
You have bought the wrong update.
Upgrading from 6.5 to 8.5 is 249 euro.
see here: Cubase: Music Production Software | Steinberg
Also, i am not confident if retrologue 2 still has the VST2.4 dll included, so i would verify that also.
If so, it will not appear in cubase 6.5.
kind regards,
R.