Over charged on my debit order

I have always had a debit order of R 436.94 with ADT security since the 15% VAT increase. I see I have now been debited R 474.09, why? I didn't have any call outs for the month of October, I haven't received a letter in regards to a price increase, so why now without any reason have you debited my account with an extra R 37.15? If you cant give me a reason I would like to cancel my contract!