Salary rate

I worked for LabCorp for 4 years and 9 months, out of that I worked alone for 4 years and 3 months. I just now find out that it pays up to $60,000.00 a year. They were only paying me $29,000.00 a year. I was doing everything alone and also micro managing the office alone. I am very upset! I have asked for a reconsiderations for my salary, but LabCorp refuse to pay me properly. I no longer work for this company. But my suggestion to a new hire is ask for the max salary they can pay you per hour. Huge company, hadly pay thier employee and work them to death.