Inconsistent pricing

DSTV at it again with charging incorrect amounts in Jan they charged me an incorrect amount, after my interaction with DDTV I was informed that the matter was corrected and a credit was done, then last month I got charged R678 which I didn’t mind as it’s a small amount, this month again I get an sms saying I will be charged R728…why that amount when I am on pricelock, the correct amount is R677, and will remain like that for the next 2 years…please correct this….