Sorry to hear that mate, the point is that the marks are there when they should not be, nothing else matters.
More like the dealer or Norton polished it to hide marks and put swirls in the paint as a result. I had a dealer do this once and when I removed polish to prep for ceramic coating the said marks became very obvious.
If they panel prep what they have accused you of applying and when the marks are still there they will look pretty stupid.
Rather than them sort it they may be prepared to pay your detailers invoice to correct it as far as possible if you have greater faith in them as in my case. Personally I would push for a new tank.
If they don't play ball, name and shame them.
Good luck with it.