WP hacked, advice needed please

Today we discovered that one of the sites we are managing just got hacked, as none of the pages inside the site is appearing.

Whenever we go to pages, all we see is the number of pages in [ All (63) | Published (61) | Private (2)] but the pages don’t appear and instead only the message (No pages found) appear

So can someone please tell me how to quickly rectify this problem as the site is down for long time now

Thanks in advance for your help and cooperation