If you signed a contract agreeing to "whatever speed I get" for that price, and then didn't complain / cancel the service IN A SOLID YEAR of having it, then you don't have any consumer rights to fall back on.
The service provided was as stated ("up to"), it was delivered, and you didn't deem it inadequate for an entire year.
Sorry, I can see your point of view, but that's not how service contracts work.
Additionally, complaining retroactively doesn't necessarily entitle you to a full refund for the whole year anyway, unless you complained on day one and kept that same complaint open all that time (in which case, why were your continuing to pay for it?).
Otherwise, quite literally I could get 30Mbps on a 75Mbps theoretical line, not say a word for 10 years, and then sue the ISP for half my monthly rental back as far as my contract start when they upgrade kit or make my line better or force me onto a better package. Literally NO ISP would bother to upgrade you or fix your connections in such instances.