1Gig Unlimited Internet Service is not Unlimited?

I moved in to my cousins house 6 months ago. I am a streamer on Twitch. Since, I have been streaming 7 yrs ago. I have always gotten the 1 gig Unlimited Internet plan. I asked my cousin to switch from AT&T to Xfinity so I can get the q gig service. She obliged,  we called together to make sure it was the correct plan. We'll, aside from still not burying the cable line that goes across the lawn, which is still there 5 months later. The 1st month, my cousin gets a text stating she went over the threshold of service. I call up immediately speak to a customer service representative. He tells me not to worry as it just a computer automated text. I confirm with him I have 1 gig unlimited Internet Service. He confirmed,  well 4 months later my cousin gets another text. I tell her don't worry it's probably the computer automated text. Well,, it turns out Xfinity is charging an extra $90 for overage fees to my Internet data. I did some research and found that 1Gig Internet Service has a threshold in selected areas. 1. Why wasn't I informed that I live in such area? 2. Why wasn't this explained when asking for & getting 1Gig Unlimited Internet service? I feel Xfinity might be trying to scam elderly for instances as this & I am very upset with Xfinity for not upholding their end of the plan I originally asked for.