Appliance not working

I bought the Safeway blender at clicks and it stopped working around November. Sent them a message on Facebook and instagram and said I can it to the store with my receipt. I did exactly that this morning, Yandiswa service provider was assisting and said she tested it with water and it is working. I told her when I try it at home it doesn’t work or it works then stops while I’m busy using it, she said she will buy an apple and check it as a blender is working. What kind of service is this. So I must go back home with the blender and if it doesn’t work return it to the store and they test it with water? What if it will work every time I take it back to the store…. Being told there’s nothing they can do is not good enough something must be done about this