Are you a prepaid or postpaid customer? 

You would need a new SIM card to get your phone connected to Koodo network. The easiest way is probably visiting a Koodo/Telus or a 3rd party to get a new SIM and reactivate in self-serve https://www.koodomobile.com/en/help/koodo-sim-support?

I'm a monthly customer. In order to transfer my old number, I was supposed to use my old sim card but I messed up. I can't receive calls. 

You could receive the code to email as well. At store, a rep can also switch it if you have proper ID. 

Are you trying to port in from another wireless carrier?

If so, you can contact your former carrier and tell them you want to allow porting and they can remove the requirement to respond to the porting text.

You may also want to contact Koodo first to cancel the port request and submit a new port request once you have spoken to your old carrier.