Nedbank are useless!

Since I became a Nedbank personal banking client in May 2017, I have been unable to make online purchases with my Nedbank Gold Credit MasterCard, due to an Approve-it error (3D authentication error). I have repeatedly contacted Nedbank about the Approve-it error I'm experiencing, and they keep saying there is nothing wrong on their side, when clearly there is! The cellphone number on the page that says "Thank you for using your Nedbank card to make your Internet purchase. To complete the purchase you need to authenticate yourself using Approve-it" is NOT my cellphone number, and every time I click "Continue, I have my phone" I get an error message from Nedbank Mastercard ID Check saying an internal error occurred. Everyone at Nedbank (via Nedbank Chat, email, and in the branch) I've spoken to says there is no error on their side, they are not declining the transaction, there's no record of me trying to make an online purchase, everything is fine with my card, the error is on the retailer's websites, etc. NO-ONE can help me, and I am beyond frustrated with their lack of customer service. If you don't want to lose your mind due to the stupidity of others, stay far away from Nedbank.