You can fight him in the bankruptcy court, or if you get permission you can fight him where the garnishment was taking place. The Chapter 13 case should disclose his assets and have a payment plan proposing to pay various creditors. He could be proposing to pay you in full and get rid of some other debt, however, he is probably trying to knock out your debt. You need some legal help to see if your debt can get special treatment so you can get paid in full in his Chapter 13.
Yes, you should consider hiring an attorney as your issue sounds like it can get relatively complicated - you have the validity and enforcement of the agreement, the nature of property involved being community and the bankruptcy to hash out.
Don't forget to check "Helpful" if I helped you out. This response is not intended to create an attorney client relationship and is based on the limited information available at the time of the response. Before acting on anything stated or referenced in this response you should consult with an attorney of your choosing and go over the specific details of your legal circumstances. My responses are also given in the context of the laws of the State of Louisiana. To the extent this comment involves principles of law governed by another state my comment merely reflects my opinion and should not be considered legal advice.
Although neither spousal support nor property settlement can be discharged in a chapter 7, property settlements can be discharged in a chapter 13 (spousal support is non-dischargeable in both). You should certainly consult an attorney to see if you can argue the obligation is spousal support rather than just property settlement.