If the exterminator is spraying something quarterly and it is not keeping insects at bay then what you are paying for is a waste of your money.
What is attracting those ants to the deck? Did someone spill something sweet on the deck? The ants are not the problem but are a symptom of something and you need to look at the why they are there.

Well we've never seen a single ant inside the house, just on the deck. Nothing has been spilled and they are pretty much everywhere, not in one concentrated area. I guess I'll mention it to the exterminator the next time they come out.

Have you found a solution? I have the same problem. I cannot use my deck at all~

Seems like you would need to have someone find the nest and destroy it.

I will try, but they may come back, I have a wooded area around my house. Is it possible the color white of the deck my be attracting them? Why are they there, it doesn't make sense~