you need to buy ant spray that sticks to their back that they take back to the nest, its sold in a red spray bottle at most outlets, spray everywhere where the nests are, be warned that they make a lot of nests, it takes time but it kills them, last year I had 40 nests in my back garden alone, after a year of use we are down to 3 nests
vigilance is the key, make sure you block any gaps where they are getting in, spray around the outside of your house, keep food off the floor