The phone number is a harassment tactic by a debt collection agency called Conversion Outsourcing.
They called me over a week ago about a bogus "debt" from Citizens Bank. I informed them that it was a mistake and that I had closed that account not owing anything, having already made deposits that covered any and all charges before account closure, and that the bank should not have charged me.
Conversion Outsourcing calls from 855-849-1984 and only lets it ring once and hangs up, or if you pick up there is dead air. They do this once per day, sometimes twice, for the purpose of harassing the supposed "debtor" and enticing them to call back.
If you call back, it can be used to confirm your identity for the purpose of debt collection. Best course of action is to ignore the calls and do not call back.
It's a really creepy, underhanded ploy that utilizes purposeful harassment of the supposed "debtor" to try to skirt anti-harassment debt collection law.