If its marked as completed in your Paypal account then you have paid. The fact its pending on the sellers account is between them and Paypal. Funds for new sellers are held for 21 days but released more quickly if they provide a tracking number (delivery + 1 day).
Even if the funds were withdrawn to their bank account they are still obliged to issue a refund if they lose a dispute. The hold is to protect Paypal from bad sellers that refuse, meaning Paypal may have to refund the buyer instead putting the sellers account into negative until they pay Paypal back.
If they refuse to send item/service then you could file a dispute for non receipt. That may impact their paypal account in some way if they continue doing so.