Pathetic customer service

I emailed them last month to change my banking details. They went ahead trying to deduct money once from my old account number and twice from my new account, causing me to incur 3 times banking costs. Fine put that down to bad timing and whatever. This month, haha surprise, they again try to deduct from my old account. Why do we request corrections?why do we have to incur unneccesary banking costs? Mtn your service is pathetic. I am very unhappy that you are costing me so much money just to pay my account due to your staff's incompetence.