why my Iturnes store cannot connect with my purchase billing

See If you can't connect to the App Store, iTunes Store, or other Apple services https://support.apple.com/en-us/HT201400. There have been quite a few Apple server connection problems lately. Among other things, in the above document, see Check Apple’s System Status page. You can check there to see if the needed server is available when you need to use one. 

Also, see your purchase history for the App Store or iTunes Store https://support.apple.com/en-us/HT204088

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.