The Invisible (2007) on Netflix

Nick Powell is an excellent high-school student who raises money by selling homework and results of quizzes to his schoolmates. He aims to travel to London for a writer's course - telling his best friend, Pete Egan, that he has already bought the airplane ticket but he has not told to his mother yet. Annie Newton has a problem with Pete, who owes money to her. As events unfold, due to a case of mistaken identity Nick takes a severe beating from Annie and her gang, his body dumped in a sewer. The next morning, he discovers he cannot be seen - he is now a spirit in a state of limbo and can only observe as the events of that day unfold.