That may be the case but it wouldn’t explain why TK confirmed the flights and gave a PNR number and the rest for a date after expiry. It would be good enough to show TK willingly engaged to perform service as per PNR and thus a formation of the contract (in exchange for using the ticket/voucher).

Consumer right laws generally give ADDITIONAL protections (like extended warranties, rights to return…). I know some of these laws in the UK as I use them to provide security against risky suppliers, but I am not aware of specific ones for airlines.

There may be one covering travel situations like this, but I would refrain from pushing “consumer rights” unless if you know the law and the rights given. Instead focus on basic contractual agreements (what TK agreed when issuing you a PNR and over the phone) AND WHAT YOU AGREED TO DO IN EXCHANGE (i.e. not seek a refund - this is what makes it a contract - give and take) and then how that was not performed.

In itself that should be enough for a chargeback or insurance claim, which are separate from any consumer rights or litigation that may itself exist.