Lie to by sales representative

I was approach by sales representative in my house,While getting internet install.He told me that he was able to get me a deal if i add a new line to my account.I told him it sounds good but it will have to be on a latter day.2 weeks later i text him to confirm again the deal he texted back i would get 700 off a iphone if i get a new number,and he will even bring me the phone to my house.I when ahead with this he came gave me the phone he explain after 3 months i will see the discount. Well 4 month later i call at&t and they told me no such deal exist!!.I try calling the sales guy and texting him but he is avoiding me.now i have proof thru the text messages that this was the deal i was told.anyone knows if i could take any legal actions from this.or any suggestions on what i can do to get the deal i was promise?