Unfotunately there is not to force a seller to sell an item, but this is very bad selling, and you can if you wish contact eBay Customer Services. Serious sanctions can be placed on the seller's account.
Explain you did not authorise this cancellation, and were very disappointed not to receive the car.
eBay will charge the seller a fee , and place a damaging defect on their account. It doesn't take many defects for eBay to remove a seller permanently from their site. eBay do not like unhappy buyers, they tend not to come back to their site to buy.
To contact Customer Services the quickest way is through this link below.
You can select a Live Chat or a Call Back option is available when the lines are not busy.
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
Lines open between 8 a.m. to10 p.m. on weekdays.
9 a.m. to 6 p.m. on weekends
@mccrossdog