This happened about a year ago and since I'm not dependent on music for my livelihood, disappointed as I was with the outcome, I just moved on and forgot about it.
I can't exactly recall the correspondence with the advertising company but they assured me that they would immediately cease issuing compliance notices on my behalf.
Beyond that I never again tried to engage youtube / content-id myself to see what's what.
I know there is a mechanism for those affected by the takedown notices to challenge them, which I guess in my case they should win, but the easier thing is just get another piece of CC music for the video.
Sucks for me but easy solution for the video-maker.