I had exactly the same experience, in person, at CW recently. Old and new passports and embassy letter were all that were needed. I have never once used an agent in over 40 hassle-free years.
My advice ? Always build a brick wall topped with broken glass or some such. A cheap pair of pliers will make a large hole in that mesh in no time at all.
Many of us could have told you that was going to happen. Thai immigration have their rules and procedures, as do all countries. Before embarking on any course of action involving the immigration authority here, best to do a bit of research first.
I must assume this is meant as a joke, in which case 5 out of 10 for the attempt, otherwise take a serious reality check combined with a hefty degree of honest introspection.
Lucky for you. Poor, unfriendly, service generally, apart from a small number of branches. I have had accounts at SCB since Standard Chartered closed their retail business here, and my impression is they are none too keen on westerners.