1600,- thb is the official fine for the landlord, if he doesn't file a TM30. If you need an extension or COR or whatever, you need to pay it for your landlord. Try to get it back from him.
I haven't been there yet. People are not talking good about Sihanoukville (anymore). Kep seems to be the better choice. While I was forced to do border bounces, I've gone to Koh Kong several times. Not bad and easy to reach by bus to trat plus van to the Checkpoint. Always good for a couple of days.
since Phnom Penh is a shithole, I recommend a flight to Siem Reap. Visit Angkor Wat. If it's about a border bounce for another 60 day stamp, you can go by van to Ban Pakkad. Start is 6.00am, back in Pattaya about 3.00pm.