Telkom overcharge

I defaulted on my debit order on the 1st of January 2020 then the payment went through on th 24th January 2020. Telkom sent me an invoice with a charge of R202 for the default with the payment made within 30 days. That is ridiculous how do they calculate their fees worst part is My payment plan is even less than their charges of R202. Funny thing is I once owed Vodacom two installments of R400 but was never charged this much for the default.