Got email saying I'm nearing my data cap, but I'm supposed to have unlimited data in my plan.

Basically title. I recently signed up for X-Class X-Gig which states it includes unlimited data. But yesterday I received a warning email saying I was nearing my data cap and would be charged if I go over.

Is this some kind of mistake? How do I ensure I DO have unlimited data and won't be charged if I go over 1TB?

Screenshot of my current plan stating that unlimited data is included: