Great Eastern Trading — Salesperson gave incomplete information on change of price when buyed on EMI

I purchsed a water purifier today, I asked about the price to the sales person he said the total product price that I need to pay. When I said I will pay on EMI, they checked on system and said the price that was said earlier( the non EMI price) but later after paying the down payment I found that the down payment that I made is an extra amount over and above product price, when I enquired then they said "EMI will cost high, then GST was not included in previous price that we said an all". I want to say as a customer we have right to decide whether to buy on EMI or by cash but that depends on the genuine and honest informations shared by sales person, why they didn't disclose the right price? Also when I said I have decided to buy a particular brand of product still 2 - 3 salespersons were trying to push another brand. Dissatisfied with this kind of behaviour, I decided to buy the product from Great Eastern as I thought it to be a genuine place to buy but very much disappointment with such behaviour.