Because i change my debit order date RAIN want to charge me again

I paid my account on 26 August - Requested to change my debit order date to the last day of every month now as per the consultant they said because i changed the debit order date i need to pay again 1 September - RAIN is *****s this is ridiculous i wouldn't recommend anyone to use this service provider!!! Needless to say that we have ongoing internet issues over and above this!!!!