Cell C charges R70 for a missing debit order of R35.

I have a cell phone contract on a contract at R35 per month. Due to financial difficulties, my debit order failed to go through. The company billed me R140 for the missed debit order, and when I asked to reverse this, they simply cut me off, despite that I have pay-as-you-go airtime and data on the phone. They cut off my sim such that I could not even make a call to their 135 support number.