The Can-US plan is available for existing customers for a while in self-serve though. which plan were you on previously and what plan did you see when you tried to change your plan?

There was a only a 65 dollar plan listed for 120 gb. I was hoping for something closer to the 40$ plan that I had. I was offered the 55 dollar plan as the lowest priced option.

Unless there was a special promotions, there wasn't any Canada-US plan that has the price of under $55, though

If you have a rep change your rate plan for you through customer service they charge you a service fee. This is outlined on koodo assist. An image of the different charges can be seen from the screenshot below. Dinh is right it seems they gave you a cheaper option than what is commonly available, however, they still have to charge you the fee.

I am ok to pay if I was having an issue. Here I could not have chosen the plan by myself. If it would have been an option for me I would have chosen it, and saved 15 dollars.

The fee was added automatically by Koodo system, rep had to make decision to waive it or not. 

In your case I think it is justified, given you saw a US-CAN plan and they gave you a promotional plan. Koodo didn’t say specifically that they only charged you if you didn’t see the plan in self-serve. It only said they could charge you for changing your rate plan.