Star Bazaar — bagasso cycle bad quality

Address:

Bangalore, Karnataka

Bagasso foldable cycle with gear was purchased from star bazaar, gopalan arcade mall banagalore, on november 2017 for 8000rs. It's totally of poor quality. First the gear shifter down. I personally replaced. Now it's the gear box itself broken. I called star bazaar, no answer. They say they arenot responsible, they only sell the product, contact the company customer care. But there's no bagasso company brand in india. There's no warranty card was given while purchasing. But they said the bill is the warranty card. I have bill with me now. But now star bazaar people are rejecting the bill as warranty and refuse to take the complaint. I need a refund back.
What is my next step, where to complain. Product t is of poor quality. It's just the loot in the name of tata brand.