Rate increase despite contract?

They have terms in their terms of service, which you agreed to upon using their services, that they can at anytime change the rates of your plan for whatever reason.  Even if they told you a certain price and that's what you expect to pay, they can bump it up 5% or they can triple it if thats what they decide to do.  They are supposed to notify you well in advance before this happens in your bill or by email, but they don't have to.  They also have a dedicated page where they post this info.  Its also in their terms that it is YOUR responsibility to check that page and the status of these rate changes and if you do not cancel your services and these rate changes apply, you have now agreed to them.

They can also at anytime limit or restrict access to the services you are paying for.  If they wanted, they could cut your service in half and charge you double for it.  You could of course cancel the services before this happens, but they'll charge you a fee for doing so if you are under contract.  

Companies like Telus like to use the word "contract" because it gives the impression that you are signing up for something with fixed terms that will apply for the duration.  In actuality its a contract that they have the right to change by using amendments for whatever reason they like. 

But there is always the possibility that this is a mistake so please do follow up with them about the issue. 

You can view more information about your specific services terms here:  https://www.telus.com/en/bc/support/topic/service-terms/mobility