You should direct them to this thread where a longtime admin (me) on the largest planted tank forum on earth says the company needs to make this right for you. Since I'm guessing you paid for a tank without cosmetic damage? For that, they need to process a refund large enough to make it worth your while and to justify the damage. Because, frankly, I don't know any bank or credit card company that wouldn't approve a chargeback or warranty claim for something like this. I volunteer to help you (or anyone else in similar shoes) with any claims necessary.
It should be fine structurally if there is no visible seam damage or stretching. But really... you shouldn't have to deal with that, regardless of brand. I've ordered hundreds of tanks like this and every retailer and equipment producer I've dealt with has made things right. Every one.
I realize you're not trying to be confrontational with them, etc, but wanted to post this so you have the option to do something if you need to and know that there will be people who can help a bit. If you choose to press them for a partial refund and they don't oblige? Let me know privately and I'll help you navigate our system, etc.