If a judgement is granted in one amount can a garnishment be for a higher amount? 

The garnishment, once in place, is difficult to have voided.  I would need to know the date that the judgment entered as you may be able to fight this on the grounds that you did not receive notice and were never properly served with the lawsuit.  in many states there are rules where you can open a judgment and fight it if you were not served properly and less than 4 months have elapsed.  I suggest hiring a lawyer to review all the paper work that you have in connection with the judgment to determine whether there is a way that you can open the judgment on the grounds that you werte never served and had no notice.  Most lawyers will meet with you for free the first time to give you an idea of the chances you have to open the judgment and try to settle the claim to avoid a garnishment.  you may also be able to modify the garnishment.  Speak to a lawyer asap.