I suggest nippon ant killer, following the instructions. The sweet, poisonous liquid is fed to the queen by worker ants. When the queen dies, so does the rest of the colony. I now use, if necessary, ant powder, which works better as the powder is carried into the nest, and any ant coming into contact with it, including the queen dies. The boiling water and vinegar has an effect for a while, but the queen is so deep in the nest, she is unnaffected and just re-colonises. For information, unless the ants are a real nuisance and/or are coming into the house, leave them be. They have a beneficial effect, their tunnels aerating the soil and allowing water to soak in whilst also allowing drainage.