Levi's India — jense

Address:

Udaipur, Rajasthan, 313001

I purchased a jense from levi's store in udaipur on offer of 30%.
But i want to exchange it because it's waist size is lesser.
But the store owner says that they can't exchange because i purchased that jense on offer scheme.
I have the bill of that purchasing please help me.
I have paid ₹2100
I want to exchange this jense with 36 waist another jense.