i bought one app "Oh sir..."

See the Apple Support article(s) below. 

Apps won’t downloaded.  *

App Store, iTunes Store, or other Apple services - If you can't connect   *

Some things you can try. 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. See the section towards the end of the article.

Reset Device. -

Contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

Apple on Twitter