As part of the conversation when I finally got ahold of the stock manager, he told me that if the terranium wasn't in on Friday, I'd be able to move my deposit onto a different tank, and that no matter what, he'd call me by the end of the week to let me know what was going on (whether it was in or not).
Come Saturday, I still haven't gotten a phone call, and I decide enough is enough and get my friend with a truck to drive me there so I can grab a different terranium. While I'm there I find the manager and explain things. The manager attempts to find my order, and can only find an order for a 75 gallon lid, and no note of a desposit. I bring out my reciept, and show it to him. I find a 75 gallon aquarium, which had more or less the same dimensions (actually a little bigger. An extra .5 inches on every side). It was a little more expensive than my original order, and I had to purchase the lid seperately because it didn't come with one, but the manager knocked down the price so it matched the original terranium that I had ordered.
So, tl;dr, lots of incompetentness from the stock manager (Not calling me, saying he'd call me and then not calling me again, not actually logging that I ordered the damn thing even though he apparently did put the order in, etc. etc.), but manager man knows how customer service actually works.
Currently using paper towel as his ground, but I've ordered some tile from a local flooring business. Glad that I didn't do it earlier, given the different dimensions of this tank compared to the other one.