Facebook processes the initial payment for orders placed through their marketplace, so any payment issues are resolved with them.
When orders are canceled before they are shipped the charge does not fully process, this means that you won't see a credit on your account but the original charge should disappear.
In cases where we refund Facebook orders, it can usually take anywhere between 3-7 business days for the funds to appear in your account. Once we release the funds we aren't able to investigate what happens to them after that.
If you experience any issues receiving a refund from the Facebook Marketplace you can contact their payments support team by following this link. We recommend sending them screenshots of the charge on your account so they can assist you right away!