Contract law and unsigned mortgage scenario?

It is illegal for them to do that, they can not change anything after you signed it. If you have a copy of what you signed, they usually give you one, your copy is proof. You need to contact a lawyer, you will probably be able to get out of that contract, since what they did was very illegal. Happen to me once. I got a lawyer, got out of the contract because they did not want me filing criminal charges on them. While they committed a crime, does not mean you have the property free and clear, just means, you can get out of the contract and move on.

I worked for a bank in the mortgage department. They can only charge what is written in the mortgage contract that you signed. However, when you apply for the mortgage the rate is only guaranteed for a specified time. Before signing the mortgage document you should have read the terms. So whatever the documents states and you have signed it and it's been registered, there is nothing you can do until your renewal date comes up.

Play it slow. Things to consider: are you living in the house? is it a big difference? If it's costing you 5 bucks a month, then obviously you can afford to work with them for a while.

Explain the situation gently, trying many different people in the network, before hiring an attorney.

And you certainly still owe for what you borrowed. Just maybe not at that interest rate.