Well, once they filed for garnishment your employer's payroll setup the automatic garnishment deductions. I'd start with talking to your employer's payroll department, telling them you filed BK so the garnishment is no longer valid, you'll need to provide documents showing that you filed. Then send copies of your BK filing to the creditor that made the garnishment and demand they cease & desist.
Your lawyer should do all the calling and faxing to your payroll for you. You will get that money back because you filing creates an automatic stay.
Here's an update on my situation. I filed for ch 7 and wasjust discharged. Before discharge I only got back $100 and I was told by my employer that I would get another $100 that was held during the automatic stay once I provide proof of my discharge. I checked with my lawyer and he said I most likely wouldn't be able to recover any of the $5000 they took even though I recall him mentioning during our concsult that it is a possibility that sometimes they can go back at least 3 months and recover wages. I'm glad to be discharged but I don't feel like the lawyer provided much help. I am still having to fight with debt holders who havent cleared my balances etc and once they filed my paperwork the lawyer was pretty much done with me it seems. Definitely a learning experience. Never want to go through this again.