have a look t what you submitted and if you do not discover what you did wrong use a reliable visa company. I used concierge in pattaya. They will have a lot of experience now. Maybe they can tell you what you did wrong but first have a critical look , maybe together with a friend at the requirements and what you submitted. It can't be too difficult to find whta you did wrong. Just three requirements !!! i did it one and half year ago. No problem at all.
the new taxlaw is not activated but does not matter. If you send 65.000 that is ok, conform the requirements. If you later have to pay tax that does not matter you could spend it on ladies too.
Koh Chang is nice but very small island. Just one road and no big stores.no Makro( just s very small one) no shoppingmall, no homepro, no big supermarket. Is a real holiday island