Cancellation and Billing

I started my contract on 15.09.2021 and was told by the rain consultants that I can cancel within 30 days and they will refund me since they deduct the the full amount upfront.

I cancelled my sim on 04.10.2021 because the signal was just bad and I couldn't use it now I am being told that I will pay the difference at the end of the month to make a full payment for October even though I cancelled within 30 days.

Whether this is their process or not, I cancelled within the 30 days because that is the information I was given by Rain. If I was given the correct information then I would have cancelled before end September.