As you've already tried multiple things and covered the basics, I would suggest trying to find some sort of coffee enthusiast group around, or maybe a bit of a fancy / hipster coffee shop, with someone who knows their way around a moka pot who could help you diagnose the issue (whether it's in the device or its usage).

Seems a shame to have had a good experience, and to have bought a moka pot, and to not get joy out of it.