Your greatest mistake here was allowing the seller to mess you around for 12 days.

You only get 30 days from delivery in which to open an ebay claim for item not as described or faulty.

30 days.

It's okay to message a seller if you strike a problem, but if it isn't resolved within about 48 hours, stop and go straight into a dispute. If a seller 'promises' a refund, it should be done there and then, you shouldn't have to wait for it. IF they are online and able to send a message, they are able to refund at the same time.

You've been played, unfortunately.

Don't ever let it happen again.

The reason you're probably having trouble with ebay is they are a pretty inflexible organisation from what i can see. Just about everything is automated. So once your 30 days are up and you haven't made a claim, then that's it, you're too late.

I have heard of occasional exceptions to the rules though so it is worth contacting ebay chat and asking them to view your messages. You can't be very many days over the 30 day deadline. I don't know if you'll get anywhere, it may depend on who you get, but it is worth a try.

Otherwise go with the chargeback etc