Customers will often cite "breach of contract" when they are unhappy with a company, and rarely know what they're talking about. Too many TV shows? I object, your honor. "Grandfathered" was also thrown around; this term applies only in very specific situations and is not a basic right applying to every or even most laws passed or regulations made.
I'm gathering from the posts of two of the individuals invoking legal terminology that the "contract" they think has been "breached" is not the ToS bomber referenced specifically, but the implied contract in the purchase of diamonds, and there is one, whenever one makes a purchase. However, that is being taken too far down a chain of events. You bought diamonds, Inno applied them to your account. You had choices how to spend those diamonds in game; you chose perhaps to buy the bps for a GB? Purchase the goods to build the GB? Purchase forge points to level up the GB? Did you receive those things? Ah, you did? No "breach of contract," then. You got what you paid for, a GB of a certain level which Inno has not taken away from you. And this is where the ToS comes in: Inno can change the ingame mechanics relating to that GB as long as it applies equally to everyone. Which they've done before, and have done again now. Too bad, so sad, no case.