Online orders

Good day

I would I would like to find something out, on my recent online order, the total amount debited on my account was 1480 but however when my order was received and the invoice said R1406 meaning there is a difference of R74, and this is not the first time this happened, even on my previous orders it has happened, and I know on your website it says the difference will be reverse into your account etc, but I have never,ever seen that happening...please advise on how this amount will be credited etc