Btw the Thai to English translation was done by one of my Thai acquaintances, it's just an informal translation, but this is what you need, to cancel the Non B extension. 👍
I found myself in similar position a couple of days ago and this Visa cancellation is not a very simple process, I didn't get any help online, so I had to make couple of trips to the Immigration office. I'm posting the list of documents that you need from your last employer to cancel the Visa extension and buddy you owe me a couple of beers for saving your time and money 😄�