they are wrong and should compensate you for all your extra costs and hassle. Sounds like you are in the right here and need to stick to your guns. Such a Shame to go through all the hassle of the Thai pass and then denied boarding. I would have been splitting nails at check-in
To be fair this is all on the Thai Embassy websites in your country which you don't state
Tourist TR entey gets you 2 months 30 days + 30 days but you may also need a visa or get visa free entry depends on nationality/coming from where and must do Thailand Pass.
Special Tourist Visa gets you max 9 months. Lot of paperwork attached to this.
Try Google and the Thai Embassy site in your home country.....it is all there