Unless the rules have changed, you're permitted to attend an MOT with the stickers attached (so whilst Tyler knows a great deal, I doubt he knows the UK MOT regs, so ignore that for now notwithstanding that the advice on H7s for UK lights would get you though; I'm just not sure you need it at all according to the (recent) regs).
The MOT regs allowed you to attend an MOT with sticker attached to your lights 6 months ago. If there has been a change, it's since then. You're very unlucky to have failed for this alone. I'd find a different testing station or go back with the sticker attached a copy of the MOT regs in hand, because the testing stations don't necessarily know the rules. You'll find the MOT regs on the internet. It's a huge document (700+ pages) but it's indexed very well. You'll find what you need quickly.