Grip Generator fails after 4 Months and about 16 hours of usage, get a R5600 bill

I bought a Grip 7.5KVa Generator from Makro on the 7th of February 2021 and we used the generator for about 12 to 16 hours during load shedding to supply power to our laptops and the network so that we can continue working during Load Shedding. In the beginning of June we had load shedding and when we turned the Generator on, sparks came out the bottom of the unit and was not supplying any power. We took it back to Makro for warranty repair and we got slapped with a bill of about R5600 to repair the generator. It originally cost us R11000 to buy the unit. Grip is saying we overloaded the unit, which is incorrect because we had 3 laptops and some wifi routers attached. Surely the unit should have overload protection on it anyway that will protect it from something happening. NOT HAPPY WITH THE PRODUCT OR SERVICE