Earlier quoted context omitted.
Isn't changing the terms of a deal without even sending you a new contract pretty much illegal anywhere sane? Even between business entities?
We don't know (but the norm is) if the original contract had a sunset clause. Almost every special rate I have ever negotiated had specific clauses about when the rate will end, even if there was no specific date there's always something about "rate is reviewed annually" or similar. I am constantly surprised by the number of people with "manager " in their title who don't know how to read a legal document. The other…
Well, that's what you have lawyers for.
Otherwise, agreed with your comment.