Page 3 or 4 of your bill should be able to explain what the issue is. If you still don't understand or want to dispute it, then you may want to try contacting Koodo on Facebook if the call wait times are too long.
I have 500 anytime canada wide minutes and unlimited evenings and weekends after 5pm. I was charged for overages on airtime for calls that were made after 5pm and only on one day. I understand if I went over the 500 minutes but from what I can see online I did not go over.