I am an English teacher working in China and I recently bought a card and credit worth 200 baht so that I may call China and the UK.
I have tried numerous times, but with no response.
I rang up and complained, and they apologized stating that the international system was not working at the moment.
My stay in Bangkok is going very well apart from this problem.
looking at a website for local ex-pats, I can see this is not an isolated instance.