Calls numerous times during the week. Never leaves a message. When you call back the number, a person answers and tells you that everything is being recorded and will use the information to collect a debt, but wouldn't give the name of his company.
This sounds like another one of those debt scams to me.
I run a couple of phone trace things on them - usually nothing comes up, but sometimes. Sometimes it is a company relevant in your life and you will see that - see who the company is - and wonder why they won't leave a message if they are who they say they are. No message left = never a callback from me.