unknowingly,I was sold a demo iPhone by authorised apple store

So, I live in India and today I went to an authorised apple store to buy an iPhone 7 Plus. I wanted to buy the 32gb variant and they quoted me 72,000 INR for it, I asked for some discounts and told them that I was getting it cheaper online. The sales person went to the manager to discuss something and he came back and said that they can sell it for 68,000 INR, I felt that I was getting a great deal and agreed but they told me that the phone they will sell me will not have headphones in the box. The sales person told me that apple also launched iphone models with no headphones included for those buyers who wanted to buy the wireless earpods. Then he showed me the box, it was sealed and it looked okay. I paid them (I also bought insurance for the phone) & they told me to unbox it, I did and everything seemed ok, no headphones were included as they said then they said they will update it to 10.1 OS. They took my iPhone and updated it and I got back home with my new iPhone but then I noticed at the back bottom of my iPhone some code was printed "IS 1352 (Part-1)" etc. I felt strange and I checked the back of the box and saw it was printed "demo - not for resale" I researched on the internet and figured that these models are not for sale but for display at apple stores. Now I feel cheated because they didn't tell me that this was demo piece, they clearly lied from the beginning.

I want to know that is it legal to sell demo phones by apple stores? And is it different from the original one? What Should I about it? Because if I knew that I was being sold a "demo phone" I wouldn't have purchased it at all.