Occuring rejection fee

I took a phone on contract with Telkom and my monthly subscription is R221.05. And last month I informed them about the change on my banking details, I was told that I will only see the changes next month as their system can only uptade my details month-end. I was advised to manually transfer the money as they won't be able to debit my new account. On the 25th of June they tried to debit the old account the is invalid and on the 26th I went to the Telkom store in Northgate to pay what is due for that month as per arrangements, and I was told to make payment at Pick n Pay of which I did. And now I received a statement stating my subscription for this month will be R423.75 of which R221.05 will be the rejection fee. I called them and I was told the fee occurred because they were unable to bebit. I asked how is that possible because they were not supposed to debit as per arrangement I was to manually transfer money of which I did. I'm so disappointed at Telkom and I informed my colleagues about experience and my other colleague told me after his contract expired and cancelled, he was billed for three months and every month he will call quiry this and it carried on for three months. I believe this is my last contract with them.