OK. Last time i was in Kap Choeng in April i was told that the immigration office there was only to process workers from Cambodia and that all expats had to go to the Surin immigration office from June.
I did renew my retirement extension in Surin in June without any problem.
I live near Rattanaburi myself and i always go to the Surin immigration office near the Cambodian border (about 240 km return trip). The local district office does not deal with immigration matters.