Generator under guarantee

On 07 July 2015 I returned a Grip Generator to Builders Warehouse in Riverhorse Durban due to the fact that it is not generating electricity, I bought the generator from Builders Warehouse Riverhorse Durban on 15 June 2015. The generator is still under guarantee that is why they had no problem to take the generator. On 13 August 2015 I received a E-Mail from Lenny Govender Replenishment Manager - Riverhorse stating that it will cost me R6012.75 to repair the generator that is still under guarantee. Or I will have to pay R500 for transport and faultfinding to get my generator back. I really think that it is pathetic to expect me to pay ANYTHING for a product that is still under guarantee. Clearly a guarantee at Builders Warehouse is worth NOTHING!! If this is the service that they give us, I will have no choice but to inform family and friends not to buy ANYTHING from Builders Warehouse that is under guarantee because it is not even worth the paper it is written on