Telkom debit order problem

Having paid telkom R345 on 14 April 2020, my bank account was debited on 20 April 2020 with the same amount. I cancelled the payment and was duly penalised with R202.70 for non payment. Why penalise the customer who pays you earlier than agreed upon? Is this their skewed logic? Upon speaking to them I was told that I will have to pay the penalty as I am bound by the contract with them which states that a debit order will run on 20th of every month. I am cancelling this service once I've used all the data I have paid them for, including the night data.