abuesing

Can anyone post FedEx's interline shipping policy with other airlines? I had a small issue with a station in UT holding a package hostage at their station due to a missing unit number on the airbill.

I was slightly frustrated when they were trying to charge me $20 to return my envelope to me or attempt another delivery, and then I was disconnected on my cell phone during the call to the station. After the first call they noted me as "being difficult", and told me they wouldn't return it to me, nor would they attempt another delivery to my recipient, even if I paid $20, or even full price at this point (the recipient is an older lady who can't drive herself). They said the ONLY option was for the recipient to pick it up.

I finally got the situation taken care at the original shipping station ( they were awesome! ). Now I am just curious about the FedEx interline policy. Can they hold your package like that without shipping it back eventually? How many attempts can they make for delivery if the unit number was missing?

As a former courier at FedEx, I know FedEx will go out of their way to deliver a package, even for interline shipments.
Thanks!