Debt Collection Payment After a Judgment

On 1/27/10 I paid a debt collector in full. On 1/29/10 I received a letter from the City Marshal that this debt was now in judgment. On 1/29/10 the debt collector received and stamped my check received, crossed out "paid in full" that I wrote in the memo and did not notify the City Marshal. Today is 2/23/10 and I found out that this judgment was sent to my employer on 2/17/10 to garnish my wages. I called the debt collector and can't get anybody to talk to me. Is there anything I can do? Is this legal? I live in NY.