Herring-Hall-Marvin Safe Co

I have a Herring-Hall-Marvin Safe. I have the combination but I am unable to open it. The dial seems a little stiff at times but I don't know if I am doing something wrong. The safe is about 5 feet tall by 3 feet wide and is extremely heavy. It has one door with the combination dial and handle. I have the Serial Number or Safe Number. Is there anyone or any place that can help me resolve this issue? The safe was mine and my husband's. When we split 18 months ago, I never opened it so it has been closed up for that long. If anyone can help I would appreciate it.