How can I find a creditor that apperars in my credict report

I pull my credict report and it is showing an old accout with ATT and it shows that the original creditor is Capital Assist Group but I can find their phone number or a way to contact them. I called the number that it shows on my credict report but they said that they don't have anithing under my name or my social security. So I contacted ATT directly but they said as well that they don't have anything under my name or my social. So how can I clear this account from my credict report?