Answer: Based on your description I am not certain what is happening to your tree. This plant is reputedly very difficult to maintain as a container plant. It is very sensitive to low humidity (probably not a problem for you if it is outdoors this summer!) and to build-up of salts in the potting mix from either fertilizer or minerals in your water.
By repotting you have probably placed it into fresh soil so any buildup over time should now be eliminated. I hope overall your potting mix is a good quality soilless mix with an acidic pH, formulated for container plants. If you added sand, I hope it was coarse builder's sand that you rinsed thoroughly prior to adding it to the mix. (And not the finer beach sand which would be salty and also compact quickly.) Most good container mixed are already formulated to do this so I am not sure why you added sand or charcoal. In any case, it should drain freely yet hold both air and moisture like a sponge.
At this point I would suspect your tree is very stressed -- whatever the original problem may have been, now combined with transplant shock. I would place it in a location with morning sun and protection from wind, keep the soil slightly moist like a wrung out sponge (never sopping wet or saturated, not dried out) and be very patient to see if it can come out of it. Do not be tempted to fertilize it to make it grow better at this point.
Without seeing the plant it is very difficult to try to make suggestions. Another option would be to try to get some local trouble shooting advice from your county extension and/or the retailer where you purchased the tree. I'm sorry you are having trouble with your tree.
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