Missing pay

I am a TCD and was asked to start doing a pickup in the evenings after my morning sort shift. The business had mostly airs but always a few grounds so I knew I was supposed to get TCD rate but I was given air shuttle rate instead. It was corrected for a paycheck or two but always had to talk to supervisor to get corrected. They eventually stopped letting me run it because of the payroll errors or so I was told but I am missing over $500 from the last week I was able to run it. The supervisor is aware and it’s been about a month since the paycheck error. I was wondering if I file a grievance how much penalty pay I will receive and if it will be TCD rate or sort rate.