Sorry to see the damage to your new board. It's fairly clear that it was packaged poorly and/or handled badly by the shipping company. Assuming that the shipper was arranged by the seller your recourse should be thru the seller. If you agreed to buy something that they will ship to you then your "implied contract" gives you every right to receive the goods undamaged and the seller has given you a reliance to get it to you in good condition by taking payment.
How did you pay for the board? If you used a credit card or Paypal you can make a complaint and they will probably get your money back.
The fact that the board was damaged is bad enough, but the other sad part of this story is that the seller and/or the shipper are refusing to take responsibilty for their deficiencies.
If you end up having to keep the board you might be able to repair it if you have access to some good materials. It's hard to tell if the damage went into the core, so I'll assume it has and that would be the biggest concern. Some cores are better when exposed to water than others, but in eother case you want to arrest any chance of delamination.
I am sure there are many experts on this forum and hopefully they will also offer ideas, but I would try to remove any loose/damaged material and then fill it with a good quality marine epoxy like West System, http://www.westsystem.com/ss/
, maybe even use some microballs as filler material. You can look at their website to learn about the various products that are good for structural repair where gaps need to be filled
The other problem is that these materals are expensive because you need to buy minimum quantities. If there is a good boat yard nearb maybe they can fix it for you since they would have these materials on hand.
Otherwise for a less expensive solution you could try "Ding Stick" which is a 2-part epoxy material which cost under $15usd for a small stick (around 8" long) which would be more thaan enough for that job.
With either material you can build a "form" on both side of the board with some stiff material so that you approximate the desired shape of the edge.
Do good prep, apply the material, and sand it out, ride it and keep an eye on the repair after you have stressed it a little. Hopefully it works.
Either of these repairs might not look pretty, but if getting the seller, or credit card company, to help you doesn't work than you have nothing to lose by trying to fix it.
I generally do not support using the forum to expose the name of sellers for their inadequacies unless
it is clear they are taking adantage of you, giving you the run-around, being dishonest, etc...so that's a decision you need to make if all options have been exhausted. But I will say that it would be a shame that the seller is not stepping up, especially if this came from a shop.
good luck with it