These sorts of rejections are especially frustrating because it's really easy for requesters to confirm participation via MTurk ID or IP address in some cases... Especially considering that this requester invited you back for a follow-up?...
Anyway, a much more effective way of getting the word-out about a requester issuing unfair rejections is to do so via TurkerView (
https://turkerview.com/). TurkerView makes it a lot easier for workers to see if a requester has a history of rejections before they even begin working on the HIT.
For Mai Anh Nguyen, yours would be the first reported rejections
https://turkerview.com/requesters/A1MGU1LKIYMOIU
The fact that they rejected you twice, on two separate HITs, for incorrect completion codes is a strong indicator that this is really not a requester whose HITs are worth doing.