Since iTunes update I cannot access songs that i have paid for, even songs that I have had for a while.
Why can’t I access music that I have recently purchased or music that I purchased before the new iTunes?
See Hide and unhide music, movies, TV shows, audiobooks, and books - Apple Support in case you've inadvertently hidden some of your purchase history. If that isn't the issue then try Empty/corrupt iTunes library after upgrade/crash - Apple Community or explain what you have in your library and what happens when you try to play it.
tt2