I doubt a large landscape and design company needs to take maintenance work. I also doubt that there is any brown nosing involved. If you know who it is then simply give them a call and explain that that is your job and you have been doing it for 15 years. That you don't appreciate loosing money because your work is done for you. They may have made a mess with the mulch on the yard and it was easier to clean it all up than to try and pick the spilled mulch out of the leaves. They probably don't know it is being maintained if it looks like a mess every time they come there. They might not even know about you at all. So take it easy and deal with it. It's your job protect it.