NUMEROUS REQUESTS IGNORED

I have been receiving mail to my private post box for a company called Pirtrek Northern Cape Pty Ltd for almost 5 years. They are large envelopes containing the usage data of numerous vehicles. I have telephoned, emailed and returned to sender - i.e. Mercantile Bank. I have telephoned Mercantile Bank Call centre on numerous occasions requesting them to notify Pirtrek and their mailing point that they are mistakenly using my mailing address for their mail. Each time I have spoken to a call centre agent I have been assured that the error would be rectified and that I would not receive further mail. Yesterday I received the mail for September and October. I also fail to understand how Pirtrek Northern Cape havent queried missing mail for almost 5 years! I have now trashed the envelopes and will not return to sender them again or bother to call the call centre. Such a simple task yet Mercantile bank cant get it right - correct and change the postal address of one of their clients.