can Scotiabank unilaterally decide to increase an auto loans fixed interest rate?

Today in the mail I got that Scotia was adjusting my fixed interest for an auto loan. Loans in good standing, never missed a payment ( i actually pay extra on it every month), it's not a hugely signifiganr amount but it's enough that I want to cancel any and all dealings with the big banks (again) if they can adjust interest like this.

Is this a normal thing that credit unions and online only banks have just shielded me from in the past?

Edit: this is the first change in 2 years, the original paperwork states it is a fixed, non variable auto loan

Edit edit: I wrote here cause I was on hold but on the phone they were very adamant that this was sent in error because there is no record, no scheduled record to increase the fixed loan. They suggested I bring the letter to the branch as it's possible records got mixed up.... which isn't ideal but they would also email me past the day it is suppose to change to confirm that it did not go up