I'm in the middle of drafting a formal complaint to the company involved in my previous post. They are based in Latvia and their terms say Latvian law applies.
Luckily there's an official English translation of the appropriate Latvian consumer legislation online. I am also quoting UK legislation which is similar.
In Distance Contracts (which your one is) a trader must make the consumer aware of certain proscribed information prior to entering into a contract. This includes informing the consumer that if he or she withdraws from that contract, the consumer is responsible for the cost of returning the goods.
The Consumer Contracts (Information, Cancellation and Additional Charges) Regulations 2013 Reg. 10(1),(4) & Schedule 2(m) is what supports that.
The consumer has to pay for the cost of returning the goods unless agreed otherwise OR if the trader has not informed the consumer of this condition.
Same Regulations but this time, Reg. 35(5).
I had a look at the STKLife website and this is the link to returns and refunds,
https://www.stklife.com/pages/returns-refunds
Can't see anything there about paying for returns, regardless of the reasons.
I would ask them to quote the exact terms they claim to mean you need to pay and give you the link.
I was advised to make a formal complaint to the company, hence my having to prepare the evidence for it.
Contact the Citizens Advice anyway so that they are aware of it and can let Trading Standards know.