Bad service

On the 17th of August 2020 I took out a contract with Cell C, I brought my pay slip and bank statement with me as they were one of the necessary documents for the process. My pay slip and bank statement indicated that I get paid on the 25th of every month and so was the contract that I signed with the lady that was assisting me.

On the 22nd of September I received a message from my phone that I debit order tried to go through but bounced due to funds that were not enough for the transaction, i then went to the store where i took the contract to enquire as to why the debit order went of early and was told that it might be because of the public holiday which was the 24th of September so the debit orders went early and i then asked the consultant why I did not receive notifications of such so that i can prepare and he could not answer. On the 4th I noticed that Cell C did not debit, i then went and paid at Nedbank on the 5/6th of October. On the week of the 11th of October I received an SMS from Cell C of my statement but to my surprise there was an additional R70.00 added on it and I again went to the store and enquired about this then they told me they will contact Cell C's head office and come back to me which they did not. On the 21st of October I went to the store again to enquire about this and the lady that was helping me explained that because I once had a contract with Cell c in the past they DEFAULTED ME to the previous debit order date but what puzzles me is:

1. They DEFAULTED ME without any communication whatsoever 2. During their decision to default, why did they not check the current pay slip and bank statement to see that I do not get paid on the same dat anymore 3. Why am I the one liable to pay for a default they decided to do without my consent. Now that for this month the debit bounced will I be liable to pay again for something I did not authorize