Cannot get MTN to send invoices

Could somebody help explain to me why it is so hard to get your MTN invoice monthly. When you try register on https://portalsso.mtn.co.za/Register which they ask you to the browser throws a "Internal Server Error has occured" message. This has been going on for the past 6 months. The emails I get sent to download my invoice take me to this site above. When I try to log in I get "Internal Server Error has occured" message. When I call them at their service center I am told to go to the above site and and access them.