I had this problem and the solution is to stay calm. You will not get instant results.
First remove any sugar based stuff and put it high up where there is no route for the ants. The powder is best I found - go right round the edge of the skirting and made sure there are no holes to the outside. Repair them if there is. Doors you need to put extra powder down - not much a heavy dusting. Leave the powder down and the ants should disappear. They only come inside for the "food".
You will not eradicate ants there are too many of them.
I have still got some of the original tub of powder that I bought.