I used an entire can of ant spray on the mound after I spread it out with a broom.
Try Boiling Water and or Ant spray or powder!
Lera, You must spray the whole area but take note, they will come back if you do not spray at least every 6 months. Fire ants just move from where you spot spray to about 2 feet over, so treat your whole yard. They will come back eventually if you don't keep your yard treated.
Here is a good article on how to treat fire ants. https://www.clemson.edu/extension/publications/entomology/turf-ornamental/fire-ant-management-in-the-home-lawn-to06.html
and another one is this, although I have never used this product it has good reviews... https://www.gardentech.com/blog/pest-id-and-prevention/simple-effective-fire-ant-control