Hi Andrew - to change your data notification preferences, just check or uncheck the boxes at this Self Serve link (login needed): Remember to make sure you're making the changes for the specific number in question.
Andrew, I had the same issue. The only choices on self serve were 50% and 90% and I definitely had a shock free data plan. I had to private message Koodo on their Facebook page and it turned out to be some type of glitch. They were able to fix it from their end so that the 100% showed as an option.