Un authorized debit order date

I took out a wifi router contract with telkom Southgate.I requested that I get debited on the 25th of each mont.on 24/11 2017 a debit order went off and came back as un paid..in December 27/12 I was debited more than what was expected,I went to the branch to query..a call was made to the call centre and I was told there's a fee for an unpaid deposit.I asked the lady why charge me for going into my bank account on a date that we didn't agree on,she couldn't give me a straight answer,on top of that I had fee that I had to pay to my bank for a returned debit.

the lady said she will escalate my query on 27/12,till this day iam still waiting..I regret taking this contract