What's wrong with the logic?

I've received a phone call from one of my colleague asking for a progress of the assignment in which I've never been acknowledged.

While asking her back on what assignment is it, she replied "the one that I spoke with your subordinate".

During the past years, I've found that this behaviour has started to be spreading out. Calling/emailing one person, but follow up the progress with another one.

Even though, the concept of the team is that everyone in the team should be able to act for one another at all times. However, in someway... somehow, it would be much better and greater contacting the main contact persons...at least it save more times.