one downlaoded album bought in Itunes is divided in two parts with differend numbers

if I understand correctly you bought an album but it's come through to your phone split between two albums with different songs in each. I had this issue after moving to Sync Library with Apple Music, one album on my Mac would get sync'd to my phone as 2 albums. For whatever reason the album level information on each song was different or became inconsistent, in particular the "compilations" flag was set inconsistently in some cases. If you go into the songs on your mac (presumably where your master music library is), right click Get Info either song by song or for all the songs at once. Doing that action alone to open the Get Info window may clean up any inconsistencies in your library; if not also check information such as compilation flag, album name and album artist are all consistent across the tracks. Once I did this I found the Apple Music sync cleaned up the phone almost immediately.