I feel like there's a lot of missed steps. Didn't you have to sign anything that confirmed what you would be doing? Did your orthodontist never say what you were paying for? It was probably just a mistake and they sent you the wrong thing.

If he said £3000-3500, then that's all you need to know that Invisalign Lite should cost you £3000-3500 max from that orthodontist. Because if Lite cost you £4,500, then what's this magical treatment that costs £3000?

I also find it weird that there's a potential £500 difference when it's always Invisalign Lite. It should always be 3,000, or always 3,500 no?

For reference, my treatment cost £3,000 for Invisalign Lite and was what he recommended, or £4,100 for normal Invisalign if I wanted to fix one wisdom teeth that can't even be seen. They are a diamond provider, and offer free teeth whitening and a discount if you pay in full. I also get two free scans for refinements if I'm not happy.