Are you a prepaid customer or postpaid (monthly bill) customer?

I misread your post. For prepaid, you can pick up a SIM card at any Koodo kiosk, or authorized TELUS/Koodo seller. Login to your self serve account and follow the steps to change your SIM card so that you don’t lose your phone number, (see third link “Replacing your old SIM card with a new one?”)

Store Locator | Koodo & BYOD

For postpaid, you should be able to pickup a replacement postpaid SIM card in-store or order one online. Note that if you purchase the SIM card in-store, there’s a $50 connection fee. When you order online, the $50 connection fee gets waived. Login to your self serve account and follow the steps to change your SIM card so that you don’t lose your phone number.

https://www.koodomobile.com/setup  click on “Replacing your old SIM card with a new one?”

Since you don’t have a working SIM card to receive the SMS verification code that Koodo sends to your phone, I would suggest downloading the Fongo Mobile app. This will give you a free local Canadian phone number. The app is available for Android and iOS devices and works over Wi-Fi (or mobile data). This will allow you to use the phone number to schedule callback using Koodo Assist and receive a callback. 

Are you a current Koodo customer? If so, you should be able to get a new SIM card at your nearest Koodo store and swap it on your Self-Serve account. https://www.koodomobile.com/en/help/koodo-sim-support

Otherwise, you can sign up for a new one, either online or at your store, and you will be given a SIM card to use on your new device. 

I am an existing monthly postpaid client of Koodo.

Sounds like I need to get a sim card. Since my existing Koodo phone works without a sim card that I would be able to have the same setup with my BYOD phone.

Essentially, I am going from an A8 to and S20

Was the old phone the Samsung A8, if so,it must have a SIM card inside. Can you check the top of the phone? I believe the SIM slot for the A8 was there.