IC Systems Collection

Recently, a collection appeared on my husband's credit report from IC Systems - it said it originated from AT&T U-Verse. We have no idea where this came from because he had not had any AT&T services for over 5 years at the minimum, probably closer to 10 years. He never received anything from AT&T in all this time saying he owed any money and to his knowledge everything was paid in full once the account was closed. We are in the process of buying a house, so this is a HUGE issue. Can someone from AT&T help me with this?