Reduce Child Support

Can someone help me understand this! So my kids dad supposed to pay $1207 in child support a month for two kids but hasn’t paid a dime. I got served today and Im just not understanding it! It says respond with an answer but respond to whom it literally says nothing? No lawyer name or address. And since he hasn’t paid any child support does he still have to owe back pay if they reduce it? He supposed to pay me directly but nothing has been received the past 6 months since ordered. He changes job so much and get fired till where I just don’t if ill ever get it and now he’s trying to reduce it. And he left a 80k job to a $22hr job gots to be on purpose. But yes Im confused on responding it.