Bad service, unfriendly staff

We bought a macbook air for my daughters 18th birthday in July using their in house finance. We also took insurance on the device should anything go wrong. Last week vertical lines appeared on the screen. We took it back to the branch at Nicolway in Fourways. They told us that they need the original invoice in order to book it in. The invoice has been misplaced as we have recently moved. The service from this point was shocking. They couldn't pick up our purchase and seem to have no record. How is this possible that they cannot find it on their system using surname or Id number? They certainly don't have any issues when it's time to get their monthly payments. It's already annoying that there is something wrong with a macbook that is less that 4 months old and now they cannot help until original invoice is found how can there be no sign of our details on their system. The device is now sitting at their store whilst we try and locate the invoice which we haven't yet been able to find. Surely there must be another way of getting this sorted