Telkom Overcharging Inappropriately

Telkom has overcharged me for making a manual payment, which is my method of payment. I made an early payment in full yet still recieved a penalty fee. As a result of this penalty fee, I now owe telkom an additional amount which I refuse to pay, as I've made payment in full for my account. My services have now been suspended and Telkom won't assist in the matter until I pay a penalty fee.