Complaint Review: Penn Credit Corporation

This company calls my dad during early morning late night during the day etc.  He is 90 years old and recently had two strokes.  I have had his pwer of Attorny and paid his bills for the last 12 years.  I finally got tired of the phone calls so I answered and they stated the usual questioning.  They said they were trying to collect an overdue debt and tht he needed to pay it today.  A red flag went up. I told them to mail me something to that effect and they asked for my address.  I told them they had it and hung up.  Who can I report them to so that someone will investigate their underhamded and possibly illegal activities.