The person said his name was jason from Northland group.  He is extremely rude.

This phone number belongs to the Northland Group in Minneapolis, MN.      *

The Northland Group is a professional debt collection agency, servicing the retail and bankcard markets, as well as a broad range of additional markets and clients nationwide.

I also had many missed calls from this # with no message so finally 1 day I answered and it was a bill collector who actually was very helpful and respectful in helping me get my business resolved.

This number has called about ten times a day for the past couple days - not leaving messages.

This man with a foreign accent called my son's mobile phone and uttered some name that was unintelligible.
My son told him he must have the wrong number, and he said something that sounded like,"Huh" in a skeptical tone. he has since called him 20 times.
What can be done?

this person has called for 2 days about 20 times.