I suspect that your existing "new" battery can be brought back to life with an overnight slow charge or a charge with a self-regulating charger. Most body shops and other mechanic shops have chargers that are time-limited and usually of the "fast charge" orientation. It could well be that their charger was too much or they didn't try another approach, but just wanted it to happen pretty quickly as it might for a more seasoned battery.
Even with a regulated charging rate charger, it might read "zero" for a while after its first hooked up, but then after a while it'll start taking a charge and the charger will be putting out about 3/4 of its rated charge amount. With time, the charge rate will diminish until the needle is bouncing off of the "fully charged" mark. It might take several hours and the slower it happens, the better.
Of course, you could get your purchase documentation and see if the seller will replace it under warranty, BUT many of those vendors will want to load check the battery first and that takes an overnight charge in many cases. In other words, if it's just a low state of charge, it's a different situation than if it just will not hold a charge or has low capacity due to a weak cell.
Also, even new batteries are not at even 90% of total charge capacity "as delivered". Therefore, if you sent the vehicle to the shop with a 70% charge, for example, and it sat and was run down (some how or another), then it might be "dead" much sooner than if it's been fully charged (meaning the charger would not charge it any further).
I highly suspect that if you take the battery, clean the terminals and cable ends (probably already done), and put it on a good self-regulating charger overnight, and then keep it charged for a while afterward, it'll probably be very useable. That time frame might not suit the body shop people so that's another something to consider too, just as buying another less expensive battery to put in the car while your other more expensive battery is being recharged.
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