When you had your surgery, you should have received a phone number to call in case of emergency...If the hematoma is truly golf ball size, you should call the number you were given for instructions.
As always, when in medical distress, call 911 or go to the nearest ER.
I'm sorry, we aren't doctors and we don't know what's causing the hematoma, so we can't tell you what to do. It's possible that heat (or ice) could work, but on the other hand, either one could make it worse than it already is.
A lot of places have terrible healthcare, but again, if you're in medical distress, please call 911 or go to the nearest ER.
Please let us know how you turn out.