Got a robo call from this # on my cell phone which is both illegal! Just said to call them back with no name of person or agency or why they were calling!

I don't respond to 800 number automated calls for any reason.  I don't care who they claim to be.  This is an extremely poor practice if they are actually calling to remind someone that a bill needs to be paid.

They are called Associated Billing Services. They are not a collection agency.  They are a billing company calling to remind you that you have an outstanding medical bill from a medical provider.

I too got called from this number.

They called me too for unknown medical bill.

They called my cell.