Your legal rights and options depend on many things, including the state you live in, so you should consult with an attorney licensed in your state to best determine your legal standing and options for taking action.
But attorneys cost money, so if you are only disputing where the money was allocated, and not the actual judgment that led to the wage garnishment, then you may want to first try contacting the creditor yourself to see if this mistake can be fixed without incurring the expense hiring of an attorney. After all, it may just have been a clerical error that is easily rectified.
When contacting the creditor, be sure to have on hand all the pertaining documentation involved with this issue (i.e., the court judgment order, garnishment order, statements on the account to which you think the garnishment should have applied and the account you believe is mistakenly receiving the funds, pay stubs from which the garnishment is taking place, and any other letters, statements, and documents you have relating to this situation).
Hopefully you and your creditor are able to correct this matter easily and without legal action. If not, then unfortunately, you will have to contact an attorney and discuss your legal options.
I wish you the best of luck in resolving this account, and hope that the information I have provided helps you Find. Learn. Save.