Assuming your in the union keep calling. If you’re not go to work. Create a case as if you are always going to have to prove things at a hearing, eventually you just may have to. Take a screen shot of your call log on your cell phone. When/if they call you, due to not showing up to work, politely verbally cut them off, ask for your supervisors email address and send them a copy of the call log. Don’t put any other content in the email. This is a classic move by UPS, the other is to just take the phone off the hook. They may try to discipline you in some form particularly if you’ve got any other attendance issues. Be sure to discuss this issue with your steward. Attend a union meeting.