Sorry to hear you had such a tough run with Custom Aquariums. Your experience differed somewhat from mine too. After my experience with them, I’m surprised to read how bad things went for you from a customer service standpoint. Sounds like a nightmare.
In my case, it did take them 3 tries to get my tank right, which is why I might hesitate to order from them again in the future. However, they were easy to work with, coordinated return shipments, and even gave me a price break for the inconvenience.
First tank shows up at my house, and there were some minor air gaps in the silicone seam between the structural seam and the interior “protective seam”. Cosmetic only, no structural impact. However, I found it unacceptable since I spent more for a custom tank and I wanted it to be absolutely perfect. They built and delivered me a new tank. The 2nd tank showed up, and it had similar issues. They worked with me again with returning the tank back to them, and they built me another (3rd) tank which showed up looking perfect.
Since I had spent a good bit of time and stress throughout this process unpacking, repacking, and shipping/receiving all these tanks, they actually gave me money back in my order for the inconvenience. So while the tank itself took a couple tries for them to get right, their customer service was a shining light.