How much did you break up the root ball, and was the plant in full leaf at the time? If a lot of root was lost or damaged that could be the problem. The only way I can think of around that at this point would be to try and shade it at least during the hotter part of the day if you can do that in any way, or at least spray it with some water during the hottest part of the day. There is a more drastic possibility but probably best to save that for a last resort.
