Samsung — Return and payment

Address:

Morbi, Gujarat, 363641

Dear sir,
I am getting a faulty power bank of samsung from book my offer.power bank charged only 2%of my mobile. So i want to return it.so tell me how i am return this power bank? I also mail to your custmore care but does not any reply from your side.plz send me your suggestion.i do power bank charged into 4 to 5 hour but not charged. After 5 hour charged my power bank mobile charged only by 2%