there is by now just 1 left: the combined Thai ''govmt'' bus with some Camb-company, running BKk(MOChit) _SmReap, daily, 8.00 from BKK. NO online booking.
The also started daily direct bus BKk-PnPn has been suspended due to very low takings for the current low season/rainy.
On talesofasia.com you can find an overview of about all connect at border links. Without stating from where to where a senseless question.