Coat oxtail pieces with the flour and Cajun seasoning, sear them in 3 tablespoons oil, and remove from the pan. Pour off the fat from the pan, deglaze with the Port, and pour off the Port, reserving it for later use.
In the same pot, caramelize the onions, carrot, celery, and peppers. Deglaze with the red wine. Add the oxtails to the vegetables. Adding in the tomatoes, chipotle, Sherry, bay leaves, thyme, and Port, and simmer for approximately 3 hours.
Season, to taste, with salt and pepper and serve.