Not exactly. We’re a common law country, and there is an implied covenant of good faith. It’s for a judge to decide if this price change counts as good faith. OP should file a complaint and let a judge decide.
Are you in the Cayman Islands? It looks like that's where the owner of the gTLD, Internet Naming Co., is based. Did you mean commonwealth or common law? Either way, their pricing is in line with other gTLD providers and there's no sign that they didn't violate any territory's regulations or ICANN policy, so there's not really any reason for a judge to rule against the gTLD provider.
A method for a more likely success to contact the gTLD provider and ask if a cancellation is possible.
The original pricing didn't break any US regulations. Of course, anyone can bring anyone else to court for any reason, but if the defendant didn't break any regulations, the plaintiff won't prevail, and publicly asserting that the defendant did so, when contrary to evidence, could leave the plaintiff liable for defamation.
It's also an awful place to start from, as a good-faith effort to settle the matter is much cheaper for both sides, and the only way to prevail when no regulations were violated.
There doesn’t have to be a statute that says “ you can’t raise your price more than x %” . That’s what common law means. The judge determines whether the contract between them was upheld in good faith.
Now if the contract says “every 5 years we may raise the price by 10000% “, there is good faith between the two parties.
If the contract says “every year we may increase the price by a reasonable amount to cover increasing operating cost” – the judge decides what a reasonable amount is.
That’s what common law means. The statutes are not the law. Judgements are the law.
A method for a more likely success to contact the gTLD provider and ask if a cancellation is possible.
Edit: It looks like the registrar got in contact with shrinks99 (https://news.ycombinator.com/item?id=49099021#49100427) who qualified for grandfathered price that was accidentally not applied.