After looking over the OP's profile and FB...
I suspect this was a Sports Card of some kind and could have been shipped from the USA to Canada using the letter instead of a tracked package.
FB left by the OP for other purchases seems to point in that direction.
So, if the Seller sent a $72.00 card via letter mail and it got stopped at the US customs it may have been returned to the Seller. And of course, there is no proof as there is no tracking...
Maybe the OP can do a chargeback, but there is nothing they can do on eBay as they waited over 4 months.
