Purchased ringtone not listed under sound settings even after restarting

Redownload previously purchased tones

With iOS 11, you can redownload purchased tones that you bought using your Apple ID.
Go to Settings > Sounds & Haptics, then tap on any sound. At the top of the page, tap Download All Purchased Tones to check for any previously purchased tones not currently downloaded to your device. You might not see this option if you've already redownloaded your purchased tones or if you haven't purchased any tones.
You might not be able to redownload some previously purchased tones.

Move ringtones from iTunes to your iPhone, iPad, or iPod touch

If you have a ringtone or tone in iTunes on your Mac or PC that you want to move to your iOS device, you can manually add it to your device using iTunes.

1. Connect your device to your computer.
2. Open iTunes. Make sure that you have the latest version.
3. On your computer, find the ringtone or tone that you want to add to your device. If the ringtone or tone previously appeared in your iTunes library, you can find it in the Tones folder of your iTunes media folder.
4. Select the tone that you want to add to your device and copy it. (You can use a keyboard shortcut.)
5. Return to iTunes and go to the Library tab of Music.
6. Click on your device in the left sidebar, then click Tones.
7. Paste your tone. (You can use a keyboard shortcut.)