Did sales Rep lie about existing customer internet bundle and if so, how can I remedy my situation?

While upgrading my phone at my local AT&T store (company store, not just an authorized dealer) the sales representative mentioned that he sees I have an older internet plan with them and that I could switch to Internet Air for less money than I am currently paying because it would be bundled with my existing wireless. I was cautious and started asking questions about the new service. He said I could order it, try it out for a couple weeks and if I liked it, I could just call and cancel my old service. If I didn't like it, as long as I canceled the new one within 30 days, they wouldn't charge me. 

Turns out, within a week, we were satisfied with the new service, so I called to cancel the old one. I had seen the new service pop up on my account and it was nearly double the price the sales rep quoted me. I figured once I canceled the old service that the bundle price would apply. The customer service representative said no, it doesn't work like that and that deal is just for new internet customers. He mentioned $100 gift card was available but not the bundled price deal. 

I asked, "so, if I cancel all internet and then start it again, I could get the bundle?" He said yes. I said, I have been a loyal customer for nearly 25 years, can't you just get me the bundle price (that i was told i would get) without me having to send all of the equipment back and starting again? He said no. By this point I am livid, so I do nothing (not even canceling the old service) and I ask him for a number where I can register a complaint. He said he had no such number. I got off the phone, mad as (Edited per community guidelines) and in tears. I called back to another customer service number and asked how I could file a complaint. Of course, I had to explain my situation, but she said she couldn't help me and said her manager would call me. He couldn't help me either and said his hands were tied. So, i asked for the number to AT&T's legal department and he obliged. That's where I am at and I am thinking about moving my business, all of it, to another company. What can I do in this situation. It's a huge matter of principle and well, $300 a year that I am losing out on.