Why did I have to pay to get a phone unlocked, so I could set up with Koodo, only to have koodo relock it? It was my own phone, and now I have to make another payment to get it unlocked again.
If you had a jailbroken unlock and then went back to stock, then yes it would get relocked to the original carrier. If you paid for a legit unlock from somewhere else, though, than that won't affect anything when you put in a Koodo SIM. iPhones that are on the Apple white list of unlocked IMEIs stay that way. Whoever told you that was wrong.