I'm fairly certain I know the company you are 
talking about.  Yes, it's unfortunate that they 
didn't put your apartment number on the shipping 
label,   In their defense though, American style 
addresses are very differnent looking from the 
Japanese style.  I'm sure we've all struggled 
with sending an IPMO to Japan,  wondering if we 
got the -cho and -ku's in the right places or if 
we should include that funny T with a line on 
top. 

Regardless, after the fact there isn't much they 
can do about it.  You're asking a company in 
Japan with Japanese-speaking employees to try to 
contact some shipping clerk on the other side of 
the planet who probably won't understand what 
they're talking about anyway.  In this case, it 
really is far easier and simpler for you to 
handle it.  Be grateful that the package seems to 
have made 99.99 percent of its journey safely.  
Getting angry with the seller only makes it 
worse, for you and for the rest of us foreigners 
trying to buy goods from Japan.

Perhaps you should be asking why the UPS driver 
didn't just stop by your apartment leasing office 
to find out your apartment number.