Online Marketplace Store India - Ordered item not delivered

It is been more than * months since i have ordered for the product Presens Medical Vaporizer & Steam Inhaler OTC *** (#om******). I have paid the full amount of Rs ****, However i have not yet received the product. OMSI is asking me to pay another Rs **** (more than ***% increase in price) of money  to get the product which is not proper by any standard of  fair business practices.
OMSI response is
"We update our shop as much as possible and **% prices are accurate. However it’s humanly impossible to update all the products and their updated prices. Because we don’t stock, Actual Price may vary when we acquire it from one of our **** vendors. If it changes, order total may change and you may have to pay extra.We don’t stock so once acquired, we can’t return the product so order can’t be cancelled."