I have been struggling with the high and unexplained charges on my account

I have been struggling with the high and unexplained charges on my account. I last stopped using my account last year in October due to this. They later started sending me apprehensive messages of legal steps. Then I recently deposited funds into the account, to fully settle what they claim I owe them. My account was then in a positive for a few days. To my surprise they started to effect unexplained charges to my account. Now once more they threaten to take legal action if I do not settle this unexplained charges. Remember I survive on a R350 SRD Grant, and all the time the money is paid into my account they take almost half of it. This cannot be fair since upon opening of this account, they said it is a pay as you use Kind of an account. Now iam being heavily charged for not using it.