The entire works is boxed up and awaiting shipping back to Sota,
That certainly seems like the best course given the circumstances.
They claim this arm works with this table. Let them make it so. If they can't, I'd expect a full refund on the table. They'd owe you that after all this aggravation.
P.S. Make sure they fix the spindle-to-pivot error too. Could that be the cause of your arm/plinth collision problem? If the arm were 2mm closer to the spindle would it clear the plinth?