Being Hacked

Hi All,
Last week i was hacked by someone in Nigeria who pretended i was in Limassol, Cyprus,
having lost my wallit and passport and asking for 950€ in my name to all my contacts.
He copied my contacts on a Yahoo address with my name, account which since was cancelled by Yahoo as i know someone working at Yahoo France which relayed back to the US.
I never went to Limassol, Cyprus but this act of piratery deprived me of 4 years of important professional emails which i had stored in gmail folders. Can this be retrieved and how?
I do not know how to retrieve these even tough we read instructions with a professional computer specialist. We need to recoup these mails urgently before a certain date, August 25th i think, if not earlier. Please reply soonest as this is an emergency, thank you. Please do not limit yourself to indicate a website as this is not cristalclear to apply to help figure out what to do. A phonenumber would be welcome at Google since published numbers in several countries do not lead to human beings but to answering machines or speachless websites. Best,
Jean-Jacques