Charged me R200 for allegedly unpaid fee

I recently changed banks. I informed telkom way in advance that I have moved from fnb to standard bank. And also they must debit on the last day of the month. Cedric confirmed that everything was in order. On the 26th June telkom decided to try and debit from fnb, however there was no money cos I have obviously changed bank. Then on the 29th June they went to standard bank to debit and it was successful (even though I told them to debit on the last day of the month). So now end of July they have charged me R200 for an unpaid fee (even though it was their fault for going to debit by my fnb account). So I means they wanted to debit me on both my account. ****** ******, cos on the same month they debited on my standard bank account. I have tried to asked them to reverse my R200 and I'm not winning. They're sending me from pillar to post.