Does anyone know how to properly hand such situation with a seller on ebay?

So I order something that was an item on pre-order, the incorrect deliver date was way back in July and the Seller of course told me he'd be sending it when it comes out in Oct around the 3rd.
Now the seller is saying item has been delayed from their supplier I believe them since showed evidence of this, but said if wanted ask for a refund so did cause no date estimation. But then it's been more than 30 days so buyback protection no longer exists, and it's been over 90 days they can't refund themselves on their side.

Dispute via bank is what I'm thinking next however it says on their to give the seller 14 days to resolve the issue. Does that mean I have to tell them they've got 14 days to send it or I will do that? Or can I just wait 14 days without saying so?
Also a little issue here is the dispute via bank would be the original amount I paid which technically would be unfair because I've already received a refund on shipping cost since it wasn't sent. Meaning via dispute I would be taking an extra couple of quid which if so what does that mean?

I won't be shocked if nobody knows like myself how to deal with this. In hindsight I should've never got into buying something like this.

Does anyone know how to properly hand such situation with a seller on ebay?
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