Unhappy RYOBI client

greetings, I am writing this with a heavy heart since i feel that i have been done wrong. I bought a RYOBI Angle Grinder HG650 at Game Centre in Polokwane around March for my DIYs, since i have a 9-5 job i barely get time to use my tools, since i have bought the grinder i have only used it 4 times and within that 4 times never did i spend more than an hour working, so the last time i was using it sparks came out and i switched it off and took it to Game Centre Polokwane for repair since it was still covered under warranty, Only to be called by Game Centre Polokwane informing me that i need to pay R269.69 for repairs. they are stating that i the customer and i quote "customer is overworking the machine causing the motor to burn" close quote, now can you please tell me how have i overworked a machine which has only been used 4 times, i feel like i am being ******** by RYOBI so as to not honor their warranty promise made to me as a loyal customer, i have many RYOBI tools which i have owned for years and they never gave me any problems until now. since i am no technical know how i feel you guys are really taking advantage of that fact as to not fix my machine and from a brand that i really love it's really disappointing and I plead with you to please follow up on this because i promise to let everyone know how you guys operate, and this shall not be the end of my attempt my matter to be resolved. and i really we can solve this matter amicably and peacefully. i Thank you