hired as acctg manager 50k year based on 32 hours per week

The company normally is 37.5 hours a week. I was an exception and hired to work only 32 / week and pay is 50k / year for the 32. The workload has now increased to the point that 42/45 hours or more per week is required to get the job done. The president does not recognize the situation and now claims that I'm paid a salary "to get the job done".