MTN service

Wanting to apply for a MTN contract online (I am on MTN pay as you go currently). Send an email with the order details. Email reads an agent will contact you. No agent contacted me so I send an email again MTN replies that I should call them. I call them all goes well until the consultant asks for my banking details for the monthly debit order. I bank with Investec so the system does not recognise Investec as a bank - how is that possible? So if you bank with Investec you cannot make use of MTN as a service provider? I have send an email to MTN 2 days ago on this matter but have not received any feedback. I would like to stay with MTN but I am considering changing service provider.