Do you still have the temporary number or the old number? Have you ported out your old number to Koodo? If not, is your service active with the previous carrier? In the case that you have cancelled your service, I’m afraid your old number is not retrievable. 

How long ago did you switch to Koodo? If it's been less than 18 months you can look up your first bill in self serve, the number would be listed on there.

You shouldn't need the old number though. You can find directions on how to change the Samsung account phone number for two step verification here:

https://www.samsung.com/us/support/answer/ANS00090882/

Ive been with koodo for just over 18 months. And I know that the two step verification typically works but it sends the code to the old number (my temporary one). So when I go to the option where I've changed numbers, I put all the information the ask but for some reason it says my phone doesn't exist. I've been trying to get this fixed but it's been a constant headache that can't get fixed.

The number I have now is the number I had with my old provider. When I got my new phone woth koodo, they gave a temporary number until I told them to transfer my old number (which was pretty much instantly). But I had to make a samsung account before I was able to tell them. So the account is linked to the old number that I've never used.

You'll need to contact Koodo directly to find out the number then. I'd recommend doing so via Facebook Messenger. It isn't a live chat, but they generally respond fairly quickly. (Don't send multiple messages before you get a response, since each time you do so it drops you to the end of the queue).

You should have received an activation email from Koodo showing the temporary number when you opened your line. Did you look through your inbox? 

I believe I got it! Thank you so much! I didn't even think about that.