Your redress is against the dealer who sold you the car for selling you a faulty car with a warranty that proved to be worthless, not through any fault of the extended warranty firm, but because the service history of the car was incomplete.

So you sue the dealer for the full cost of the repair plus what you paid for the warranty. Law here: www.honestjohn.co.uk/faq/consumer-rights/

Never buy a used Porsche without a thorough interrogation of the ECU, which will show up problems such as the engine having been over-revved.