Log into your self-serve account and view the details of your bill. There are likely overages that you have accumulated in either minutes or data or perhaps roaming charges. Nobody here can answer your question specifically because nobody can see your bill except you.
If you see charges that you don't agree with, you may contact Koodo and dispute it with them.
Bills don't just go up on their own.:-) As Humberto said there is an explanation, in addition to his list check if yo upaid your last bill, that sometimes is the simple answer for a higher than normal bill. :-)