Unjustified Charges on My Telkom Account

I have a 24-month contract with Telkom, with a monthly debit order of R650 scheduled for the 15th of each month. When the debit order failed, Telkom attempted to debit the amount again on the 30th of January. However, I have now received an invoice stating that I owe R1,500.

Upon contacting the call center, I was informed that I have been charged R850, which includes penalties. According to my contract, payments are required between the 1st and 30th of each month. I do not understand what this penalty is for, and I would appreciate clarification. This charge seems unreasonable and unfair.