CellC - Daylight robbery

Cell C did a sales pitch to me on 15 August 2023 to upgrade my contract. I decided to go for it and how much I have regretted this decision. The issue is:
My old contract monthly subscription was R109 including VAT.
The new contract amount agreed to was R119.00 including VAT.
Hold and behold, in my September statement and debit order, they debited me R176.57 and they claim this is a prorata from 16 Aug to 31 Aug. How do they get to this amount, they simply cannot explain. Even if you take the full new contract amount for August which will be R10.00 (R119.00 - R110.00), it will not come to R176.57.