Have you tried Amdro? A very small amount of this bait, sprinkled gently over and around the mound, will kill off the entire population of the nest in a matter of a couple of days. I've never had it not work, as long as I was careful about not disturbing the nest and as long as the Amdro was a fresh batch.

Amdro should not be used IN vegetable gardens, but can be applied to the outside of the garden, where foraging ants will find it.

(I've not re-read that old post about boric acid, if that's the one you're referring to. So if Amdro has already been suggested, sorry.)

Rhizo, Amdro wasn't mentioned or if so I missed it. Thank you for your info and I will try that. I am at wits end trying to get rid of these ants.
Thanks.

You'll only need a small amount for each mound and I'll emphasize (again) that you need to be careful as to not disturb them. What you will see in a few seconds (it's fun to watch) is a few worker ants come out and take the little granules down with them. In a matter of a few moments, all signs of the Amdro will be gone.

After a few days, it will be a dead nest.

Store the Amdro in a cool, dark place (I keep mine in the laundry room rather than the garage.) but try to use it all up within a couple of months. It does not last long once opened.