To be honest, I am rather frustrated as well.
I was hoping that CI would be reasonable in this matter and honor their original agreements for you.
Legally, their contract is between us and them, and while they may be subject to Vumatel's agreement, we as the end customer should not be held to it.
What is also clear from this thread is that they are not interested in keeping their existing customers since their only response was to tell you to cancel your line and sign up for a new contract at a new price with no regard for what they have actually agreed to with us as customers.
I for one am looking into other ISPs.