I searched for the same some time ago and didn't find anything. The only one way is to call them, but it may not sort your issue out.*
In your case additional problem is overnight in ATH, in many cases (connecting flights from SOF for example) these tickets are unbookable via A3 website.

* Wanted to book SOF - ATH - FRA via A3 website. Flight I found is available only in GoLight, but I prefer to pay a bit more and have it in Flex tariff. Called A3 and after 15 minutes research they only said they are sorry but they cannot book Flex for me as "system says no".