Greenbacks Orders

On 24/12/2015 I logged into my Greenbacks account and bought 2 x products worth 40 000GB, I still had about 7000GB to spare, but decided to use that later. On 28/12/2015 I received an sms: Insufficient Points for your Greenbacks redemption request. I could not do anything about that at that time, but followed up on the issue this week. In stead of finding out what went wrong I was accused of making the wrong choices on the website. They told me I was trying to buy the products from a account with insufficient Greenbacks. I explained to them that it is impossible to do, you can't get pass Checkout if there is not enough Greenbacks. I even supp**** my receipt showing that the sale went through on the correct account and that the error was on their side. My points is back in my account, but both products that I bought are now no longer available and I can'g get them again.They just told me they can't assist me further, but I can speak to the complaints department. How is this service ? I have been a loyal Nedbank client for years, had and still have MFC financing, have a current account, credit card, personal loan and a overdraft and it means nothing ! NO Help, just excuses ! Useless!