Good luck with that. Immigration at (Bangkok airport) entry points seem to have wildly different policies from provincial Immigration offices. Or did you contact Immigration at that particular Bangkok airport? (If so, please share the response, as, I'm sure, many AN members would be very curious to hear about it...
You're not banned, but if I were you, I would either go with 'fast track', or, at least, get a visa from a Thai embassy/consulate. (Alternatively, stay another 6 months, or so out of Thailand.)