My bill due date is the 17th of every month but my billing cycle is on the 28th of every month. What is the difference between the two?
You billing cycle indicates the month the bill covers. For example, your bill due yesterday was for regular monthly service from April 28 to May 27. It would also have included additional charges (purchases, international calls, etc.) from March 28 to April 27.
You service is billed in advance: on April 28, you were billed for the next month. As a courtesy, AT&T says you don't have to actually pay that bill for 21 days, i.e. the 17th.
Award for Community Excellence 2019 Achiever* *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.