I just bought the game on 5/24/2019. There was no informatin regarding Activision shutting down support and only being able to play the game songs on the disc. I really enjoyed the Guitar Hero series and hoped to be able to continue playing it with new content being available for download.
Sorry for being blunt, but most likely Activision will tell you they will not help you. I received mine for xmas 2018 and because I missed the window to file for the refund that is what they told me. I just found out about the refund today, because I got tired of checking the website "For any announcements" after 3 months and missed the ~60 day window of opportunity to file for the refund. Now I am filing a complaint with the Better Business Bureau. Good luck.