Call back again. This time during the automated line say "Agent" and it will send you to an agent asap. Then ask to speak to a supervisor, the rep will want to know why so just be honest and tell them you need to have a supervisor use the "M2" upgrade on your 2nd line for an early upgrade. Most likely they will just ask the supervisor for you and process it. If they don't ask for the supervisor on duty.
If that doesn't work try again. it took me 3 CSR's and 2 supervisors before I got the right rep with the right supervisor to make it happen. Some reps just don't want to help, most do. Always be nice and don't get angry and yell at them.