Do you have access to another WiFi network where you can try? That has worked for several people.
Try a restart.
Restart your iPhone, iPad, or iPod touch
Try a forced restart.
Reset Device
If necessary
Hard reset
Do a backup and try a factory reset. Then restore from your backup.
Restore to Factory setting
Backup - Restore your device from an iCloud or iTunes backup
If necessary, contact iTunes Support. Either use the form or scroll to the bottom of the page in the 2nd link. Follow through the screens to get a chat or telephone option. You may need to pick a problem that is slightly different than yours to get a chat option.
iTunes Support
iTunes Support – world wide