Cancellation

I'm trying to downgrade on my DSTV account, the app will not allow me to downgrade, hence I called the call centre and the lady who was helping me said I can not downgrade now, but I tried to explain to her that I will not be able to afford the quoted amount at the end of the month that is why I am trying to down grade, according to my knowledge multichoice is prepaid they should have cutted my saverces after the 12 when the money was due