I've been trying to do so at odd times for three days.
EVERY SINGLE TIME it was busy.
I finally got fed up with it, and just kept hitting redial. It took me about 15 minutes of solid redialing, but I got in, and navigated the menu to oppose AB962.
Just to test, I redialed again for a few more minutes and couldn't get through.
Step 1: Call 916-445-2841
Step 2: Press 1 for English.
Step 3: Press 2 for commenting on a bill on the Governor’s desk
Step 4: Press 2 for AB962
Step 5: Press 2 for Oppose
Step 6: Repeat as necessary (preferably once or twice a day).