Debit order more than it should be without notification

Vodacom deducted R100 more than what my contract subscription amount is on 01 September 2020. Apparently somewhere in the fineprint (to which I obviously agreed without my express knowledge, because... who reads ALL the fine print, right?) this will be done when a debit order bounces. Hands up for those who did not experience this during #covid. They now have me by the ***** in the sense that I cannot cancel or get out of my contract in any way whatsoever unless I pay an exorbitent amount of money - more than my handset is worth. My only option is to cancel my debit order at the bank and let them blacklist me since I don't want to give them another cent. The trust is broken and no matter what their counter-offer or special discount would be to retain me as a customer, once my contract is over I WILL remove them from my life completely and spit on their branding.