Data plan

That's how prepaid works. If you buy a plan and then change your mind and buy a different plan you have to pay for the different plan. If you had noticed during the purchase process it warns you in red letters to wait until the end of your cycle to avoid losing service related to your existing plan.

Hi Yeisy0! There are recommendations for changing your AT&T PREPAID plan. 

As @formerlyknownas shared, it's advised that you make changes to your AT&T PREPAID plan the day before your current plan expires. This helps you avoid losing any of the remaining services of your current plan, including Rollover Data or your high-speed data usage allowance.

For more details about finding the AT&T PREPAID plan just right for you including using our automated phone service to select a new plan, check out the details under Change your AT&T PREPAID plan using our automated phone service when you visit Choose or change your AT&T PREPAID plan.

We hope this information helps. Thank you for reaching out to us.

Lar, AT&T Community Specialist