so what should u do if you are innocent, your record in Immigration is clean and the airline keeps telling u that your are not without providing any evidence? They can do that to anyone.
My old passport, which I used in 2015, has expired. This time, I used a new one. The airline contacted the Thai side and told me that I was blacklisted. They also provided a chat message from a Thai official stating this. I don't think this is an airline mistake. It is from the Thai side.
Please don't laugh because this situation could happen to anyone. Take a look at my picture; I have both entry and exit stamps, and I didn't overstay. All I can guess is:
1. When I left, the Immigration stamped my passport but forgot/failed to sign me out of their system. So, according to their system, I am still in Thailand, for 8 years.
2. They mistook me for someone else.
Considering that my name is not well-known, I believe option 1 is more likely.