AT&T prepaid unlimited $45/month

AT&T is running a promotion, for $45/month you get unlimited data, text, and talk. The original plan is $65 but you get $20 off with autopay.
They say you have to open a new line, but I called customer service and told them that T-mobile is offering unlimited for $50/month and the gave me the full discount.
https://www.att.com/prepaid/index.html