You had an RCT. I hope it was not done twice by the same dentist. RCT's vary tremendously according to the dentist and country. In the US doctors are usually poor at doing RCT's for various reasons: poor training, trying to finish quickly, having less visits,etc. Generally getting dental care in the US is very risky. It is literally "pot luck". If you read any of the dental posts from "dentists" on these sites and know anything about dentistry, you'd find that most of these doctors do not know what they are talking about. They know very little science nehind their claims.
To do a good RCT you need good equiptment relative to the situation. The tips of the tooth must be accurately found and the canals sterilised. Did your doctor sterilise and wait to see if you have pain before filling the canals. A good RCT should take at least a month to assure a high probability of success. Many doctors just clean and fill and "good luck" to you, and then after it fails you need an endodontist to overcharge you for a "retreatment". Most American dentists are wreckless..and I write this with experience. I also teach in university so personally I get my care overseas. Unfortunately I get stuck here getting care and sure enough I get the same problems I read here. I get help till I run overseas. There are good doctors here. You just have to spend a fortune to find them.
It would be best to have it checked by an endodontist but it could be coincidence that the crown repair and pain returned at the same time. You may want to go discuss that with your dentist and see if that may be related. If not, I would recommend getting a specialist to evaluate the area.