Stores aren't going to offer exchanges/refunds on these types of things. The only way I could see it happening would be if it is the store's mistake, as if you asked for Public Mobile voucher but were given one for Koodo. And even then, it's only going to happen if you notice and point it out immediately, before leaving the store, or perhaps even just walking out and walking back in 2 minutes later. Even simply going home and then coming back later in the day severely harms your chances of getting an exchange, as while it's possible that a customer never looked at the receipt until later, the more likely scenerio after some time elapses is that it could be customer error.
Now, I really have no idea if you were given the wrong voucher by mistake by the store employee or if you asked for the wrong one. However, the problem with the Koodo voucher is that they can't really sell any returned voucher because someone could have written down the code and by the time they sell it agian, it could be invalid. At this point, your best bet would be to give it to a friend who uses Koodo prepaid or to sell it privately.
