Useless Postman!!! need help?

ok heres the problem there is a new post man and he keeps delivering my mail to other people and delivering other peoples mail to me. Im scared because someone posted my mail through the door last night and it had been opened i mean how f**cking dare they!! if i had gotten someones elses mail i wouldnt open it nosy b*st*rds before i managed to get the door open to see who it was they were gone. This postman keeps doing it and im soo frickin mad now im scared that he may have delivered my bank statements to someone and i dont want my neighbours knowing all my bank details and what i earn etc anyways I was waiting for ages for my student finance form to come so i can sign it and send it back and if i miss the deadline i dont get my student loan i swear im gonna punch this post man in the mouth what can i do?!? who can i complain to??