Lawnmower issue

Very disappointed in Makro. We bought an expensive lawnmower from them and the other day it wouldn't work. We'd used the lawnmower a total of four times and in the middle of the fourth time it just died. We took it back into Makro and they've now informed us it's an issue with the oil. We haven't ever replaced or topped up the oil as we were informed it needs to be done much after just four times of use. They've said because the problem is the oil they won't cover it in our warrantee and we need to pay R2000 to fix it. How is that possible? We must pay so much on an already expensive lawnmower because of oil it came with? We've barely used it!