So hang on:
1) You were late for the Lifetime pass (presumably kickstarter) yet paid more than those with the pass? That doesn't make any sense:
https://www.kickstarter.com/projects/1461411552/elite-dangerous
Kickstarter backers paid £80+ to get the lifetime pass (Premium Beta/Alpha). The base game + beta retailed at around £50 same as the Horizons expansion mentioned above..
From what I read that makes your story an impossibility, It's possible you bought the base game + beta post release so you paid
less. Anyway, lets chalk that up to bad luck and move on to #2.
2) When Horizons first went on sale the lifetime pass was offered, it was £130 (arguably very inflated but hey ho). I know this because I agonised for over a week since at the time I was on a student budget and it would mean very limited "study related alcohol" for a long time. Either you missed the news and therefore bought the horizons upgrade after the LEP had been withdrawn or you didn't see it offered.
This was on sale for 4-6 weeks around 5th August 2015 (from my store receipt and here: The Lifetime Expansion Pass was removed from the Store on September 14th 2015).
https://forums.frontier.co.uk/showthread.php?t=172800
Assuming you were unlucky with the timing (lets say you missed it by a few days again) you could have sent support an e-mail, they are generally pretty nice people and if you'd explained your problem with missing the kickstarter etc they may have made an exception. If you were after October you have only really yourself to blame for not keeping up with the news, I mean 4-6 weeks isn't exactly a short time, I was in the same boat having missed kickstarter but reading the newsletter every week kept me in the know.
In any case you could have held off on the expansion altogether, sure you'd have missed out on content this year but if you were determined to get the Lifetime pass it'd have been the logical route to hold off for 12 months and splash out once.
Overall though you've paid probably ~£100 for 2 years content. It's not exactly a rip-off compared with other relate-able games (mentioning no names). From my perspective bad luck + your own fault is to blame here not Frontier, I may be wrong but that's my impression based on my analysis above.
One thing I can say 100% for sure is that you originally paid
less than backers did, either you backed at a lower level or you bought the base game, both of which were cheaper than the minimum backer level for the LEP..
