@Paweł *****
if the bus works, then fine. However, chances are you'll be catching a taxi (shouldn't be expensive) or a share taxi (same thing but sharing with local passengers) and then a van from there to Surin. I'm not sure whether there are flights out of Surin these days. You might have to go to Buri Ram, but that's such a long detour (probably 3 hours by public transportation from the border) you might as well go direct to Bangkok, which is like 7 hours from Surin by bus.