It is a poor branch of Immigration. Usually there is total confusion and a lot of very rude officers who do not help you in any way. A lot of shouting incoherent instructions and pointing.
It looks like as mentioned above, you needed the TM30 form to be completed to get the extension, which I assume is technically the correct protocol. The hotel should have done this for you but many of them don't bother. If you're going to immigration the next day I would always check with the hotel, some will just say "can not" which means they aren't going to do it because they're too lazy. Booking in at a chain style hotel will probably fix this problem and ensure the TM30 is done.
Just on a side note, they actually fine people for not having TM30 all the time at Jomtien, usually 800 baht so you actually got off light