If worse comes to worst, you can Return the phone -- on your own dime-- as Buyer Remorse.
Your seller described the phone correctly, it was your error that made it (possibly) unusable.
Start by asking the seller politely for a Return for Refund.
Remember when you send the phone to use a Tracked service.
https://www.canadapost.ca/cpotools/apps/far/business/findARate?execution=e1s1
You may as well spring the extra $1.50 for Signature Confirmation. Worth it, seriously.
When it shows returned the seller can refund with a click of his mouse.
He'll probably also Block you, but that will have no effect on buying from anyone else.
If he is difficult about this, come back and we can show you how to get refunded without his cooperation.
But nicely and politely is the way to start.