I ordered 316 but 304 was delivered and it was cut before the pay docket arrived and I'm now stuck with the 304.
If you paid for 316 tubing and got 304 then you paid far too much. The price
difference is almost shocking. 304 SS is popular for ladders and structural items. It is strong and cheaper but will rust if left unattended. In fresh water
it can do OK but in salt water
you have to stay on top of it as Gord notes. Good 316 could be left alone for several years at a time.
If you can validate the order you deserve a full refund. Anyone that is in the business knows the difference. Asking you to accept the order without a serious refund is not something you should accept.