Incorrectly debited

Vodacom debited R240.00 instead of R208 and the call center agent offered to return the R40 in airtime or rectify the statement, I said they should rectify the invoice, but that was not done. When I call to follow up , I am told it was 1 gig of data that was sent to me, I did not get that data, and as per my knowledge a gig is R150 not R40.