Buyer or seller to contact RM re undelivered item?

[ImFreeToDoWhatIWant]

That's it really, seller has proof of postage but wants to send it to me as the buyer to chase up with RM. It's her responsibility right?

Yes
Until the item physically gets to the buyer, it's the seller's responsibility.

RM won’t engage with you. Their contract is with the seller.

If the seller isn’t being cooperative, and the item hasn’t arrived by the latest date of the delivery estimate then just open a not received case with eBay ASAP, you’d be silly not to.

Thanks. She's insisting its up to me so I've opened a case as it's now three days beyond last estimated date.

Have you checked the sorting office if it is Royal Mail? It might be waiting there for you to collect or arrange delivery.

Sometimes people claim an item not received and get a refund, then arrange re-delivery and get the item too, that might be why she isn't keen on chasing it for you. Yes it is the seller's job but it is up to you to find out if it is waiting for delivery.

She's insisting its up to me so I've opened a case

Good. You can’t argue with stupid!

its up to you to find out if it’s waiting for delivery

Well, no, not if there hasn’t been a card left, it isn’t. And if the seller if that bothered then they can just as easily find out by googling the sorting office and calling to enquire themselves.

I wouldn’t waste my time making a special trip or sitting on hold for ages trying to call, if no card had been left.