Cover your food with plastic bags or other recipient, cover the kitchen sink with a table cloth when you are not using it; basically erase any source of food or water.
Buy "Baygon, Insecticida Mata Hormigas en Aerosol" or similar in a supermarket; when you buy the poison ensure it says "hormigas" (ants). The poison for other bugs (like cockroaches) that you can buy in a supermarket will not kill the ants.
Do not apply the poison over the food
. Apply the poison on entrance doors, toilet grids, or wherever an ant might come from. If this does not work you will need an stronger poison or to call a fumigator.