If you have them, then legally you're ok and owe Rogue nothing. But if you have them and HRMC say no import duty has been paid, pretty sure they can come after you, if they choose to. As you said though, Rogue have sent the invoice, not customs and excise so I wouldn't bother too much.
Newkid sent me something through the post a month or so ago, I got stung 40€. Buggers wouldn't give it me until I paid up and if I didn't, it was getting sent back to Blighty. I've had a few mates who've been stung in the last few months too, birthday presents etc. I'm still looking at ways to get around i