MP3 files not importing into Apple Music

Can't add folders (albums) into Apple Music that have mp3 files (songs). I tried physically changing the extension to m4a, but that did not work. Only solution was to put the cd into the player on the PC, and make sure the import setting was AAC Encoder. The frustration is that I have about 800 CDs in this library, and had them all on my Iphone. Lost the entire library during one update, and I am trying again to import my music onto my IPhone again. I do NOT want to have to re-import all those cds. Its bad enough having to physically add them to Apple Music again. Any advice?