The seller should have automatically gotten a "defect" when s/he cancelled the transaction, but the lie s/he told blamed you and avoided that. "Defects" are the primary tool eBay uses to weed out bad sellers, downgrading the selling status of those who get too many relative to their sales volume (as opposed to having to pay employees to actually investigate to see how likely it was that the seller had a legitimate reason to cancel vs. deliberate policy violations).
Report the lie at https://www.ebay.com/help/action?topicId=4850 I don't know if eBay will do anything about it (give the seller the defect s/he should have gotten if s/he had taken the blame him/herself, keep the cancellation blaming you from counting toward your Open Transaction Limits) but it's relatively easy to do it that way.
You may leave appropriate (calm, factual--if the seller said that x was the reason say "seller said x. . ." so people don't think you are just jumping to conclusions) feedback to warn future buyers/bidders. If the usual links have vanished, go to anyone's Feedback Profile (doesn't matter who, click on the feedback score in parentheses behind the username) then scroll down to below the last comment on that page to find a "Leave feedback" link that doesn't vanish (it brings you to a list of items you can leave feedback for).
eBay will not "force" the sale. Cancelled is cancelled, and they don't have a goon squad to go out anf forcibly put the item in the mail. Theoretically you could sue the seller for breach of the contract of sale (for the difference between the auction price and what you ended up having to pay for a replacement; even the courts won't force "specific performance" except in rare situations), but that is almost never practical.
