How to write a letter to a company

Hello everyone. I have a question. I just want to write a fan letter to a music company called ''Avex'' i have the adress of the company but i don't know how to write it down so that they know for which group the letter is.Could anybody explain me how i have to write it down? i need a quick answer please help me!!

My sister represent entertainers from USA that has recordings with Avex or Eibekkusu Gurūpu Hōrudingusu Kabushiki-gaisha, have about 60 subsidiary companies, so it is best to send directly to the address below. Substitute the singer name from "BoA to "Ayumi Hamasaki-

"BoA-san"
AvexTrax Artist
Avex Group Holding, Inc.
3-1-30 Minami-Aoyama, Minato-ku,Tokyo,
Japan 107-8525

Thank you very much for the quick answer i'll try like this ^_^ and could it be that the staff didn't give the letter or that the letter didn't reach the group??

Normally in the entertainment industry all fan letters are assigned to a public relation personnel/secretary,.. with so many fans delay in responding is normal. Also, Avex with so many groups mail can get lost. Good luck trying again.

Thank you for your advise..i won't give up ;)

now i have 2 psot address from "Avex" the first is : .....107-0062 Tokyo and the 2nd one is: .......Japan 107-8525
whic one is correct if i want to send a letter to "TVXQ"?? 107-8525 or 107-0062??