left a letter in mailbox stating a package needed to be delivered to me and to call them back at this number to schedule delivery. Called the number but got no response.

I just got this same letter too. Did you ever find out anything? Seems bogus.

Real delivery services usually leave a  sticky note.  These coukd be from a water softner
company based on similar posts on 800notes.

Postcard size notice says they have a package for me. Does not reference any company name or any return address. If you have a package and it doesnt cost anything and its beneficial for goodness sake deliver it to me!!! Seems like it maybe the latest scam. I did not call the number.

It's a water softener company. They say the package is an extra large bottle of Tide laundry detergent. My guess is they're just trying to get biz to test the water.