Repeated calls to a number on the Do Not Call Registry.  Does not leave message.

Repeative phone calls and leaves no messages

Who is this?

Citi Bank collections

I was already expecting a call when the phone rang around 9:20 AM  eastern.  All that appeared on my phone was "Incoming Call". That was nothing compared to hearing one continuous ring that I heard. I was able to find the alleged number that called when I checked the call history for my number. I can only imagine what this was about.
I only hope this is not the start of calls from maggots looking for people I have never heard of.