Purchasing an add-on is a two step process.
You should be able to use it instantly.
1-First you need to add the $ to your account and (you did this - great!)
2-then add the add-on to your account. (now, go back and add the addon, it should show up under the Plan Details of the account)
SO does the US Roaming add-on display under your Plan Details on his account @Razzy
Or does the amount of the add-on display under your Available Balance. If it does, it hasn't actually been purchased, just the funds added.
To purchase Add-Ons using your Self-Serve account, follow these steps:
Have tried all that.
@Razzy - are you trying to add the same addon you are currently using or just recently ended (10 days ago)?
If so, there is a glitch, where you need to wait the full 240 hours from the add onto your account date. So either make sure it has been 240+ hours ago since you last one as added (of the same type), or ask CSA to add it for you.
CSA's contact here: https://www.publicmobile.ca/en/on/get-help/articles/contact-an-agent