Canceling Debit to paying cash

I took out a cell phone contract with Telkom Mobile after being called by one of their outsourcing agencies. I took it out January this year and was released from my work the following month, I called Telkom to let them know about my employment status and kindly requested that they should stop debiting my Bank Account cause there is no longer funds, because every time they try and debit it bounces and adds over R200 on my Account. I stated that I'll pay cash every time my Account is due, they refuse. I asked to make a payment arrangement regarding the amount owed which is over R700 and apparently I don't qualify for an arrangement, Telkom says I need to owe them over R3000 to qualify for an arrangement... So I need to let my account run up and owe Telkom R3000 for me to start making some sort of arrangement to in keeping my account up to date with Telkom??? This is totally unacceptable really!!! All I'm asking is to stop debits coming through to my Bank Account and I'll see through that my account is paid and my service I'm paying for at Telkom to be reinstated because this ridiculous really... PLEASE HELP!!!