S.P.
This will sound like the strangest advice, but it worked in our house that had ants constantly (and none of the traditional remedies worked). I cooked a recipe called 40 cloves and a chicken. Essentially it used 40 cloves of garlic (about 2 heads of garlic) with a chicken, cut up. The garlic smell lasted in the house for a couple of days, but the ants never came back (even after the smell of garlic was gone).
If you don't want to cook the chicken, maybe you could bake some cloves of garlic in your oven (you probably do not need 40 cloves) to see if this will work for you.