Account payment via credit card

<p>I signed a legal contract with Vodacom in which I chose to pay my account via automatic deductions from my credit card every month. Now my credit card expired and when I phoned in to give them the new expiry date on my credit card I was told I cannot pay my account with automatic deductions from my credit card any longer. I need to go into the store every month or sign a debit order. How can Vodacom change a contract as they wish?</p>