INABILITY TO CHANGE A POSTAL CODE

After 3 years of continued phone calls, emails, submission of FICA documentation, Computershare are still unable to get our postal code right. 1st we had 0001, then we got a letter, on their letterhead, saying they'd changed it to the correct 0072, but on phoning them today, they have 0007 on their system. If their person who does data input can't put in four consecutive letters correctly, they should not be working there. HOW HARD IS THIS? Needless to say we get no mail from them as they are happily sending it to a WRONG ADDRESS. I now have to pay to get duplicate tax slips because of their complete incompetence. And they just shrug their shoulders, pass the buck and we get nowhere. There are no managers/supervisors to talk to and Customer Complaints, well I guess no one works there as they never answer the phones. The level of frustration is unbelievable and I'm totally dumbfounded at the level of incompetence. Maybe that's why no one answers at Customer Complaints, there are too many...