Dear Prerna,
You are in a truly unfortunate situation.But don't give up as you don't have a choice but to assert yourself.I mean assert your individuality,self esteem,privacy etc.Such people are a unavoidable nuisance and exist in every organisation.It is just like you can't choose your neighbours so you can't choose your colleagues too ! But your's is a government organisation and hence it should mandatorily have a committee to address cases of sexual harassment.You make a written complaint to the head of that committee.In case there is no such committee ,write to the top boss of the region or the organisation itself.Give details about how you have approached managers at different levels earlier.If still nothing happens then write to the National Commission for Women.Believe me, it may stir up your professional life initially but the final outcome will surely be better.