Messed up Accounts

Vodacom double charged me on my invoice and then they insist on charging me a pro-rata fee for a month that I received no data or airtime or minutes, No they want to put my account on hold how can you pay for something you didn't receive from a zero balance bill to 900 in one month whe my monthly payments should be R500. I sent an email logged a dispute but they insist on a pro-rata fee for services not rendered.