Unless my eyes are playing tricks on me, the box itself may have been made out of 3/4" MDF, but the cover that was screwed on was definitely not 3/4" MDF. At most it looks to be 3/8" or even 1/4" MDF. IF this is the case, then your claim will more than likely be denied. If I took a piece of 1/4 or 3/8" MDF and dropped a 40 lb. box onto it with no support under it, the MDF would snap like a toothpick. Am i'm willing to bet something like this happened.
sorry the pic is upside down, from a friends phone, but it is 3/4". honestly not sure what kind of "wood" it is, been a long time but mdf has much smoother grain than that if i remember correctly.