Fees charged

Called the call centre yesterday. Asking about arrears amount that i see on my statement. Consultant said it is fees or interest for late payment. I advised nadine i would like her manager to call me and explain to me how they charge an account that they received payment on. Seeing that the 25th was a public holiday and they deducted the 26th as there was no funds i made an internet transfer on the 30th as my funds only became available on the 29th. How can i be penlised for paying before the first. How do they work out these charges. Nadine couldnt explain this to me and neither has her manager called to explain. The account is not in default so there is no letters sent. When they called me once i told i made eft payment but still they went to my account on the 31 st to deduct a second time from my account. So all the bankfees and now this arrears balance showing is costing to much. Its obvious with all the public holidays of march late payment will be received. I want this charges cleared from my account. Its unfair to charge a client that is paying.