Nina. I don't think it is worth trying to save.
The original leaf spots and other issues it had prior to the repotting were most likely caused by not enough sunlight and/or soil that was getting too dry. Repotting did not address either of those issues but has created new ones. Replacing soil damages tiny roots and should never be done. The pot is too large and that makes root suffocation very likely.
If you get a new one, keep it in its plastic nursery pot, place it close to a sunny window, and water it as soon as the surface of the soil feels dry to the touch.