Mac and Mac models are picky about the RAM the Mac needs to see and use.
As you have found out, the 1067 speed RAM will not work in your year and model iMac.
You need the 1333 speed RAM.
If, you can return the RAM for a refund, do it!
If not, try online Mac RAM source and seller Crucial memory. They have a table that matches your Mac to the correct and reliable RAM. You may need to contact them to see whether or not they ship to South Africa, though.
If Crucial dpesn't work out, here's the specs for your year and model iMac that you need to seek out and purchase.
Maximum Memory 32 GB (Actual) 16 GB (Apple) Memory Slots 4 - 204-pin PC3-10600 (1333 MHz) DDR3 SO-DIMM
Based on the iMac model info you provided, you do indeed have the wrong RAM modules in your machine, and yes that is causing the crashing. Increasing the amount of "wrong" RAM to 32 GB will in no way solve the problem. You need to purchase and install the correct 1333MHz modules. And I would never shop at that store again.
If the iMac you purchased was new, it came with the correct ram from Apple, but it sounds like the releller removed the factory ram and replaced it with slower ram. If the machine was used prior to your purchase then someone along the way switched the factory ram for slower speed ram. In either case the store where you bought the machine should be liable for providing a working computer with the factory specified components.
If you get no satisfaction dealing with the store, be sure to purchase the correct ram for that iMac, purchase from reliable Mac specialists such as OWC and Crucial. Do not buy ram that is for PCs as it is usually too inaccurate in speed and timing for a Mac. Ram that has been found by users to particularly bad comes from Kingston Value Ram, PNY, and Corsair Vengeance series. Those ram create a lot of problems.
Make sure you get the correct ram for that iMac. You can find specs at http://www.everymac.com