Billed for data not consumed due to poor network quality

I deactivated my rain subscription on 9 September 2020. I have already advanced my reason for that (poor connection in Bloemfontein). Why am I being charged R250 even though I have not used the sim card for the whole month?

The poor explanation I'm given is that the SIM card was active on their system. How is that possible when the Sim card has been removed from the router and there's no data consumption?

At the time of the cancellation one their consultants said I'll only be billed for the data used on a pro rata basis. Today I'm told "sorry" the sim card should have been cancelled at that time. ****************!