Scam calls from 866-969-1631?

I got the exact same call from Florida number 813-607-5631. It asked me to call 848-458-5253. I knew it was a scam but called just to see what would happen. It played the T-Mobile jingle, had me press a button to get to "other" and the guy did not ask for any verification, but he knew my last monthly payment amount and date. I would get 50% off my bill for two years, and the catch was to pay 8 months up front.  He said if I agree to the promotion I would not have to pay right then. I then called the main T-mobile customer service and the guy refused to commit to it being a scam. He said that "salespeople often have better promotions than we do". What??