Changing my messaging paln

I've been trying to update my messaging plan and it is not allowing me to do so online. It tells me to call their customer service number, which I have now done 2 times. Only to be put on hold for 45 minutes and then hung up on! I understand they are busy, but this is ridiculous! I refuse to pay for any messaging overages since I've now tried multiple times to change my account without any help!