Vodacom *****ing money via debit order

I cancelled my contract with Vodacom, signed the final agreement and paid the final amount. However, Vodacom still took R245.41 off my account on the 02/05/2019 as well as R838.86 on 01/07/2019. This resulted in there not being enough money in my bank account for my medical debit order - which leaves me exposed.

How can one fight against such a big corporate that is domant in South Africa and does not care for the one individual?

I asked them about it today and was given a number to phone - no reponse and no action.

Once again - I lost.