Many promotions are for a defined period of time (like a 6-month or 12-month promotion), and if you have a promotion like this you will find a message on your bill letting you know how far along you are in the promotional time period. Your bill will say something like, "expires 10/02/2023" or "month 31 of 36."
Discounts are different than promotions, and generally do not have an end date. These discounts will remain on your bill until you change your services in such a way that the discount is no longer applicable.
You will find most promotions and discounts on your bill in the Details section. Depending on what products you have, this billing section can be called Details of Your CenturyLink Packaged Services, Details of Your Internet and Home Phone Charges, or Details of Your Internet Charges. Sometimes, the discount or promotion will show up in the Additional Charges and Credits section of your bill.
How will you find these promotions or discounts? They are generally shown as a dollar amount with a minus sign in front of them. For example, "-$10,00" or "-20.00".