It's not a cap. If the tower is congested you are deprioritiezed (lower priority) and run at a lower speed and only until the tower recovers (seconds, minutes or more), many use 100GB+ and never notice being deprioritized (or it's so minimal that many don't care).
Rember the Golden Rule: Treat others how you would like to be treated.
Just because my answer does not solve your issue (or agree with you), it may still be correct information...
Stating a fact about how something works, is NOT taking sides, it's just stating a fact...
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Award for Community Excellence 2019 Achiever* *I am not an AT&T employee, and the views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.