The problem is you raised the water volume when you added more soil. The container is holding too much water and locking out oxygen. You could take out as much as the soil as you can to lower the moisture level in the pot, just until the soil dries out a little. Make sure to be very gentle when removing the soil not to hurt or disturb the roots. When the plant dries out you can return the soil but don't water it until the plant has adapted. Or you can take the plant out of the large pot completely,and remove all the new transplanted soil it the roots won't be damaged, and that will allow all the roots to get air.
When transplanting a new plant only water the inside of the container and leave the new soil dry until the plant gets used to the transplant. After a couple of weeks you can water the outside of the new transplant.