Online nightmare! Most Inefficient online retailer

I've experienced shocking service from Zando on two occasions within a space of a few weeks but the one that sticks out is the one I had today. I purchased while the 25% off shoes was on and made payment as soon as I got to checkout, I paid using a voucher of R600 which was given when they couldnt honour my purchase and refunded my money with a voucher and the balance was paid with my credit card. After receiving proof of payment via my banking app, email and SMS Zando sends an automatic reply that my goods are weren't paid for and my order has been cancelled. This is not on and I believe incidents like these lead many consumers to thinking online purchasing is a **** and causes more issues rather than making life a little simpler. I now have to wait till Monday as they do not have any consultants working on the weekend. So my R1500 is just hanging somewhere. I will not cancel with my bank as Zando needs to wake up and provide me with these items irrespectively. I am very sceptical about shopping online and its these bad apples like Zando that spoil the production of healthy and efficient service from online retailers.