Formal complaint to DSTV MultiChoice

I paid my monthly subscription on the 22nd of this month of November, but today the 28th of November I came back home and found out that my account has been disconnected. When I contact them they say I am owing R211,96. I asked them how because I have been paying the same amount and they didn't alert me of any shortages. My due date is the 25th of every month but they disconnected today. Normally when there was a shortage in my payment they would inform me immediately. They say I have been paying less than what is expected all along that's why the amount has increased to R211,96 so my question is why they have not disconnected me all this time because according to them I was paying less than what was expected. My question is whose fault is this?