Telkom are ****** and reaping people off.

I have heard bad stories about Telkom and I must say they are a horrible business. I have been trying to change banking details for months through their agents and online, but every month they debit the old account. The worst is I payed my account earlier than the debit day. On the 25th they went to the old account and it bounced cause there were no funds,meaning that if there were funds. I would have payed double. They have the audacity to charge me for bounced debit order while they got payment for that,so I'm punished for paying my account early?