For Vistana owners that buy direct, their Bonvoy number is automatically added to their ownership profile. This goes back to the old Starwood and SPG days. Those old SPG accounts remained linked when SPG became part of Bonvoy. I suspect yours isn't linked because you bought resale?
Direct purchase (and requalified/retro) Vistana ownership comes with the ability to convert to Bonvoy as well as automatic Bonvoy Gold. Resale owners don't have the same benefits. I haven't tried adding my Bonvoy number to my Vistana ownership profile yet. If you call, let us know how it goes. I recall in the past that people have called to try to have it added and were told it can't be added for resale owners. Others have had success. YMMV.
As for getting elite night credits for Vistana stays, I just make sure our Bonvoy numbers are on the reservation at checkin.