Vodacom contract

I have a contract with vodacom and phoned their customer service to ask if I cant make a cash payment or eft to them instead of the debit order monthly because im currently unemployed. The customer agent who assist me suggested to rather not pay my account on due date and pay it later ,because they are unable to change the method of payment. Since when are they unable to change it ?because I remember changing it in the past . So I must rather pay R100 extra for a debit that didn't go through ? Customer service is rediculous