I took a short trip to Bangkok (Friday to Monday). Passing through the Koh Kong boarder point (Cham Yeam - Hat Lek). No problems on both sides. But now if you hold a Cambodian E-visa in your passport, you can only obtain two Thai monthly entry stamps via land crossings for the duration of your twelve month visa.
When you enter Thailand, walk down the left hand side of the street for around 200 yards, you will find mini buses going to Trat. 120Baht. The mini bus will leave when full. So maybe a little wait.
Then the arrival at Trat bus station, there are large and mini buses leaving to Bangkok (Ekkamai) every hour.
I took the large bus departing 220Baht. 6 hours. Returning the buses run the same every hour. I took the mini bus 5 hours 250Baht.