Get your money back. Regardless if they built it to Sundowns specs it was not built to what you wanted. Did you provide a design and/or cutsheet when you went? If so do you still have a copy? You dont build a box the way you want too just because you're a shop. The customer is always right even when wrong sometimes. They might of not liked your design or felt like it wouldnt perform better than a box built to Sundowns specs. But that doesnt give them the right to just change the design without speaking to the customer. Use your words and be cool headed, something should get resolved.