Cell C acted contrary to agreement

I was contacted by one of Cell C's telemarketers who managed to sell me a data/router contract telepathically. The agreement (of which I have not received a copy via email as promised) was that the debit order will go off on the last day of the month. I then received the product via courier, to my surprise the debit order went off on the day I actually received the package. Because my bank account did not have sufficient funds the debit order was returned of which my bank charged me a fee for this. To my frustration I then called Cell C to find out why the debit order went off earlier than the date agreed as per our agreement and why I have not received my agreement via email as promised by the telemarketer who sold me the deal. I then insisted Cell C needs to be deduct the fee charged by bank because they debited my account before the date agreed and hence they are liable for this fee. I was told that they will listen to the recording and get back to me. It's been three days and have not had any response from them. I really think their after-sales service is poor as this is my first time on their network .