How old is the bag? Do you have any pictures you are willing to share with us?
Since you have the receipt, I assume that you are the original owner of the bag (and that's always a big plus). Therefore, I second what
@Pebli suggested, which is to take the bag to another boutique. In case that's not possible, you can always return to the same location and ask a different SA to examine your bag. It's worth the hassle.
Unfortunately, whether you have been using the bag or not is somewhat irrelevant: if the bag is older, it is unlikely that Louis Vuitton will exchange the item or offer a credit (as you know cracked canvas cannot be repaired). But in some cases, we have seen exceptions. So try again. If the damage on your bag is ruled "normal wear and tear" a second time, at least you will know where you stand.
Good luck!