Why does iTunes delete already downloaded music from my phone?

i don't have particularly large music library, have, have purchased through itunes (or uploaded cd years ago).

on ios11 , itunes 12.7. purchased new album, added playlist , synced phone. not did not of newest songs dl phone (while connected imac cord), deleted downloaded songs phone! use computer manage songs , playlists. create/purchase whatever want computer, , sync phone. never syncs.

not use or subscribe apple music (and never have), , have feature turned off on phone. why apple start putting songs in cloud without me asking? how can stop happening? , why when sync playlist computer says have 312 songs on refuse add in extras, though says synced....my phone playlist shows 297 songs. know songs missing, won't transfer through sync....

syncing duplicates playlists on both sides, though i've made changes on computer side , there nothing add phone computer.

have automatic downloads music enabled on phone. on itunes sync screen on computer, checked music sync.

can't figure out way on phone find music they've thrown cloud can redownload phone. frustrated!

 

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