Lale,

Man , ur in in OPT right now and those dickhead at USCIS have a record that u already graduated..U r already in OPT , of course it is F-1 but since ur Studies are over , i don't think u will be granted new F-1 visa on the basis of Ur I-20..So talk to ur International admission office and i am sure they will have a way out..If necessary better consult an immigartion lawyer, rather than jeopardise ur carrer..We r not an expert on immigration thing, just giving u suggestions based on what we know..

Hurry and talk to the international admissiion office at ur university..hope they are good.