I had the same problem. Didnt renew the first time, let it lapse. They were not too happy about that either;). But must have done around 5 trips as well. At least now there is an immigration on Koh Chang and I dont have to go to the mainland. Wasted a lot of time (and that of our witness).
Totally get it, also happened to me. If its of any relief, it will get better after the first time. They actually smile now, gave me a cooky and some instant coffee😅. Hang in there!
I would then definitely check out the Chinese area. Find a place close to Song Sawat. Great for walking. Lots to see, do, eat and drink. Every first timer I show BKK I also take on the bicycle tour. Loads of fun and you see BKK from a whole different side. Google Co van Kessel Bangkok. Have fun!