Over billed multiple times

This is probably the 5/6th time that I am doubly billed for top ups. Each time I do a top up, I pay for it immediately. Yet, at the end of the month, I am charged again for that same top up. Once I message the WhatsApp hotline (which is supposed to be user friendly and efficient), I am told to phone the helpline. Once I do that, it takes a very long time to eventually get a hold of someone. After an exhausting back and forth of trying to get the money back and chatting to this and that person, sending bank statements (which wouldn’t have been necessary if the admin was sorted out from the beginning), it is said that it will be added to my account. This really messes up my credit score.