the head and the block were not faced properly before installing the new gasket. Idiot Mechanics say ke ji part ka fault hai. it is his fault. and he is experimenting on your expense. Also partly it is your fault to because these cars are not like the 74 Corolla which can run on water for all eternity. these need proper coolants!
Buy a genuine toyota part bhai. toyota is selling that for a reason! which city are you from?