How can I pay a debt collector if I get a hold of them?

My husband printed out his credit report, and on it he had something that had went to collection. He finally figured out what it was, but cant get a hold of the company his credit report said had the debt. There was no phone number listed on the report only a name, Jefferson Capital LLC. We have looked on the internet and called every number we can find, but only get recordings with no response. What do we do to settle this???