iTunes Library uploaded CD's

I would really like to use Apple Music, but one time I got a free trial. I was going to subscribe but needed to change something in the billing going forward so they said I had to cancel and then sign up. IMMEDIATELY upon canceling my iTunes library, which contained about 20 gb of uploaded CD's that took years to acquire and upload disappeared. I worked with multiple levels of support and level 3 or 4 tried, but ended up basically giving up and stopped responding. I did get a good portion of the music back, but some is gone. From a couple of moves after loaning CD's out and such. I don't want to repurchase everything.

Does anyone have instructions on how I can attempt to use Apple Music again without losing what I have? Thanks in advance for any insight! Is it as simple as backing up the current file and moving it elsewhere?

My thoughts are if I knew the file name I can move it and rename it so I have that to fall back on, and at some point if I stop the service I can go back to that file? I know I would lose all downloads from Music...unless I purchase then. Which brings up another question. If I do purchase how do I maintain and merge to the iTunes file I have saved? Maybe just a sign to not use the service. HA