Billing mess after upgrade

I have had a long standing query with Telkom about my bill. I upgraded to uncapped fibre at a cost of an additional cost of R100 a month, but when my bill arrived (which was supposed to be prorated) the cost came in at R100 ABOVE the more expensive package that I was upgrading to. When I queried this (in June), I was finally told *in September* this was because there was usage on my bill... well, come now, it's a line that is in use and over which I have no control as to when you effect the upgrade. But if my old package cost R100 and the new one R200 a month (for example), and you prorata it (correctly), it can't come in more expensive than if I had had the higher package FOR THE WHOLE MONTH. Unless the calculations have not been app**** properly to all. I have sent requests back for proper clarification, but have been stonewalled, so I am venting here!