Sorry, just mentioned the airport one because I was familiar with it, I've always been Chiang Mai-based in Thailand. I don't know which office deals with which problems...
I understand your concern, but even in the (allegedly) corrupt world of Thai officialdom, I can't see how they could get away with a threat to deport you...
you have a legally obtained and paid for visa,
they stuck the wrong stamp on, it's that simple.
I was the victim of an attempted scam by Lao/Thai customs a while back, completely without foundation, but sometimes it's not a case of who's right and who's wrong - it's who is in the position of power. I got away with it in the end by the skin of my teeth, but I learnt my lesson - always thank the Thai official trying on the scam for his help in sorting things out for you
Anyway, do drop by and let us know how it turns out!