Sold me inferior gearbox and guarantee breached

I purchased a second-hand automatic gearbox from Gearbox Warehouse for my Daihatsu Siirion 1.3 Auto and was assured that the box was in working condition. The box was bought with a 30 day guarantee that should there be a fault in the box then it will be replaced/refunded.<br> <br> The gearbox was provided and upon fitment at a service professional, it was notified that the gearbox was leaking. I called Ettiene ***ner of Gearbox Warehouse) and informed him of the matter, he advised the seals to be changed & provided these. After driving the vehicle over 3 different trips totally approximately 40km the gears on the box started to slip, this was two weeks after purchase & fitment.<br> <br> I communicated this fault in the box to Gearbox Warehouse and was advised refill gearbox oil, it was agreed then as well that if this did not remedy the situation then the gearbox will be replaced with another one. With no luck after replacing the gearbox oil, I have made endless attempts to obtain my money back or replacement. Ettiene is refusing to assist and is now blaming me insisting that I have damaged the box.<br> <br> I have spent R 7,500 on this box and R 3,500 for fitment.<br> <br> PLEASE HELP ME GET A REFUND/REPLACEMENT