Another day. Another 'rip-off''.

I have had an Mtn contract for a number of years and this is not the first complaint I've had with this provider. I am being ********** by poor accounting practices by Mtn. I've tried to get assistance by speaking to the agents at Columbine Square branch who tried, and failed, to get a satisfactory response to my query. I was billed on 27 Aug 22 for the amount of R 134.78 (Period from 27 08 2022 to 26 09 2022) for My Mtn Choice 20 GB. On 28 Aug. 22 I upgraded to the My Mtn Choice 40 GB. On receiving my Sept. 22 statement, I noticed that I had been charged the new tariff of R 216.52 for the same period as on my August 2022 statement (Period from 27 08 2022 to 26 09 2022). This means I have been charged R 134.78 for the 1 day between my contract expiring 0n 26 Aug.22, until I upgraded and renewed my contract on 28 Aug. 22. How is this blatant rip-off practice allowed to go on unchallenged? I urge each and every one of Mtn's customers to scrutinize their statements/invoices so as not to be "RIPPED-OFF" as I have been. Imagine a few hundred. a few thousand, or more customers from Mtn's client base of millions having this done periodically! A very tidy profit in the millions??