Telkom charging extra on the contract for late payment yet diligently payment to them are made in advance.

Telkom have been deducting or adding extra money on my cellphone contract in addition extra charges whilst I have a portfolio of evidence that I puy them prior to my payment date which is on the 15th of every month yet for the last 4 months they charge me for late payments. I can assure as indicated with POE that I do indeed pay my account well in advance every month. After submitting emails, to date I have received zero correspondence from them. I've been a client of Telkom for the last 12 years and yet they are failing a loyal client.