You have to really go to work on ants.
They are fuckers and are also armed, resourceful and harding working.
Treat it like a military operation or you will fail. Remember they have numbers on their side.
Personnally I use this tactic.
1) Recon - Find all of their nests plus more important try to track the routes they use to get their supplies back to their nest.
2) Raid and the ant powder are needed for this shit. Get the industrial powder. This shit kills cockroaches as well so it usually means certain death for a bunch of fuckers ants.
Ant Powder
3) Hit in to all nests in one go plus hit the routes they use to get supplies, nothing worse than surviving a tradegy than finding out you cant get any food as some fucker has put poison down on all your favourite tracks to the shops.
4) Seal up all the cracks into your house. Pull out the fridges and shit like that and seal between the wall and floor.
This usually does the trick.