Vanishing Promotion & Gaslighting

I signed up for the Home Internet for the promo of $50, it included a free mobile line for the first year. So, I moved my phone line over. After I completed my mobile order, there was a promotion to add an additional line for $10 a month for the first year & then it would go up to $20 after. I wanted to add my husband, but he was a family plan through AT&T so it took a few days to get all the info we needed to get his line transferred. Now, when I went to add this line - the promo vanished and now shows $20 a month. I called Xfinity and talked to multiple people who just gaslit me the whole time. They said, "This doesn't exist; it never existed". I know what I saw and now feel crazy that they're telling me my eyes were lying. Customer service was also rude throughout the call, escalating things and making us very upset. Mind you, this was our first interaction as a new customer and it was not a good one. They would have had a very loyal customer had they just honored the promo that I saw. After my free line is up, I am jumping ship - they lie and gaslight you and don't work with you. I'm just wondering if anyone else saw this promo, am I actually crazy? Because their customer service team seems to think so. I wish I took a screenshot - from now on I will.