1.
It shows up as purchased on the Itunes app
Then check your Music Library -> Recently added.

Or try to redownload, see -> Redownload music -> Redownload music - Apple Support
2.
I wanted to use it for my ringtone
To make and/or use a song as a ringtone, you must first make that song suitable for a ringtone.
See the following Apple articles:
Create and manage ringtones
Create and manage ringtones - Apple Community
Create a ringtone of your Logic Pro or GarageBand for Mac song
Create a ringtone of your Logic Pro or GarageBand for Mac song – Apple Support (UK)
Create Ringtones in Garageband
Create Ringtones in Garageband - Apple Community