Do creditors have to cooperate?

I have received notice from a CA that they intend to garnish my wages for the full amount (over $4,000) that I owe. I have sent the company (not the CA) $100 checks in the past but they have returned them, stating that they want the full amount and not what I have offered. Now the CA has said the same thing. Being in California, does the agency HAVE to work with me or can they wipe out my income for two months to satisfy their request? I am also going through a divorce and have been paying alimony and child support. Thanks in advance for ANY help.