Instacart/Facebook review: Food delivery

There seems to be a considerable discrepancy between my orders and actual deliveries. While Instacart over extends its billing process to accommodate any subsequent order changes, I have received no updates from them to indicate final billings. Granted, I do get emails stating my credit card will be credited back according to initial billing within eight days, which I find un acceptable, but my receipt for my purchase comes within a few hours. How do you bill and credit an account in a few moments. I know it can be done. I just don't for certain if it is being done.