After installing we get "no signal".
Two things. "No signal" on a modern TV usually means the device connected to the corresponding input is either not configured right, is not set up for the type of cable you're using to connect its output to the TV, or the TV input "source" hasn't been switched to the actual input you're using. You mentioned a VCR, but I would take that out of the picture to simplify your troubleshooting, and just work with the converter box and the TV. If it still doesn't work, at least that means the VCR has nothing to do with it.
Then, it would be nice to know for sure whether the converter is sending the TV the "no signal" message, or the TV was doing it on its own. If you get the message and then disconnect the interconnecting cable, and the message stops, then we know the message is coming from the converter. If it stops, the that means the TV isn't even seeing the converter. See, we are just cutting to problem in half bit by bit, to determine exactly where the problem is.
Second, I sympathize and have little patience for a customer service rep that would give up so quickly. If the converter needs an antenna, then the CS rep should have advised you what kind of antenna it needs,and how to make sure its connected right. If a CS rep gave me such poor assistance, I'd return it for my money back and buy another converter. Its hard to know enough details to prove out exactly what is likely wrong, but these steps should at least help isolate some problems. And if it is the converter, at least you know one brand never to buy again.