Civil Summons

My 90 y/o grandpa has a civil summons filled by Midland Funding LLC for a debt that he did not take. Somebody has used his SS# and got a credit card is what it looks like. They filed this summons a year ago & I contacted the Lawyers & told them he didn't get no credit card & that he was going on 90 and could not hear or see to do such things anyway. So they said ok and never heard anything again until they filled this new one. I feel like they are trying to get a default judgement against him cause with his age & health he would not be able to argue or file an answer if this summons hadn't have been delivered to my Dad and I got to see it. If it had been delivered to him he would not have understood or been able to read the summons himself. What do I need to do to get this company to stop harassing him and causing him stress and anxiety once I had to explain what all this was. He is a 5 by pass heart surgery and has a difibulator his heart is so bad. The debt is only f0r $713.88, but he didn't get the card so he should not pay a dime. What can I do to help him?