You paid for an 18 head, they didn't provide one as far as you can tell. The damage to the numbers is unusual for sure, I wouldn't point fingers but there is no reason for it. So since they didn't provide what they said they would, you should get all your money back. OTOH if they sent you an 18 head and you didn't want it, than it would be perfectly reasonable for them to charge shipping and a restocking fee, since the screw up was on your end.

I would do a charge back, and than simply move on and get a head from another vendor.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200