Ryobi **** guarantee

Bought a ryobi baby grinder at buco somersetwest not even 3 months ago .It has a12month guarantee.I have only used it once ,cut one 1.5 linear metres of plaster and pop it blew .I took it back and they charging me R530 to fix it .It only cost R350.They say the guarantee only applies if a part fails....The whole machiene failed.If i cant cut a wall for one metre with this product put it on the box ...This is faulse advertising and the guarantee if **** .Dont buy ryobi the guarantee is ****!!!!