Unauthorised debit order amount

I have been a premium Dstv customer for more than 15 years and debit order payer. I opted for Black friday special where I was going to pay R999. Then in december my services were discounted 2 in a space of a week whereas I have already paid for that month. Then from december they charged me R1300, and the following months. I complained and nothing was done. I spent more than R300 on airtime trying to resolve this issue. Nothing was done from their side until i sent email to cancel my subscription. Now they are demanding that I pay R3800 if i want to cancel. Why should I pay if they are the once who breach a contract. The contact I took out was for R999 per month not R1300 per month. I dont want anything to do with this company ever again. They ******* people, they add, subtract and add and subtract on your invoice and you end up confused. They charged me twice for the re-connection that was their fault. I have been overcharged for the past three months and then they tell me that they only over charged me with R100. I dont want your services anymore and I dont know why should I be penalised for your mistakes