Unfortunately, it happens to a small percentage which make it through quality control and checks. These are mass produced luxury watches, not a hand machined, polished, finished watch by a single watchmaker from start to finish.
I understand your frustration and disappointment in purchasing a watch with your own money and it did not work properly for more than a few months. But it is getting repaired and will be back on your wrist soon.
I get you believe Omega should swap your watch for a new one since they sold you a defective product. But at the time it was sold, it did not have the issue. The issue showed up a few months later.
It's the same as buying a car and something breaks three months later. Do you expect the dealer to swap cars since something broke on yours? No, they will take it to the repair shop and fix the issue. This is the same thing Omega is doing with your watch.
Sorry to hear about your experience but it will be fixed soon.