Well, if you have any personal information on the account, then you should call sony immediatly. They can give you the account back…because they can track the person using your account last, which would be the hacker and they can ban his PS3 from doing anything, then they can change the password themselves and everything and give it back to you…but if I were you I would call sony, tell them someone hacked your account. They will ask you questions and they will ban the hackers PS3, then tell them that you want to delete your account and make a new one. Dont worry, everything you got will go onto the other account. You would want to delete it because the hacker and get a new ps3 or tell his friends and then they would hake you again! Here is the number for sony, call and talk to them and they will take care of everything!
Sony Computer Entertainment America
M-SAT 6:00 a.m. – 8:00 p.m. PST
Sunday 7:00 a.m. 6:30 p.m
Hope this helps!