Urine calcium in the 800's is rough. While your urine calcium will come down a bit over time while being on a thiazide, about the best I have seen in trials is 50% reduction. 400mg is still too high to build bone. I highly recommend you watch this video from this really good nephrologist on idiopathic hypercalciuria https://www.youtube.com/watch?v=FN9VWgCda8c . You probably want to see someone like Dr. Coe that specializes in nephrology and kidney stones.

That all said, I'm surprised your T-scores have been stable over your testing period. Perhaps the high urine calcium is recent or a messed up measurement.