Thanks for the replies all. Yes, I have requested a refund and as I paid with Ping, thought this would be fairly straightforward. And yes, I did wait the obligatory 6 days for the “seller” to respond (they didn’t);and I did reply to TM that the trade had not been completed - I then received this:    “We’ve again contacted this seller with your concerns and encouraged them to come to an agreement with you directly and from here we’ll assess your case and will be in touch with you within four weeks regarding this matter and your eligibility under Buyer Protection. We’re experiencing higher vo...

Lastly, I believe the seller did indeed stall the refund process by firstly ignoring TM emails and then falsely claiming a problem with the courier. My thanks to Diz at Disputes for sorting this out for me. 

An update: I received the full Ping refund yesterday. This was settled 16 days following the first dispute filing. The seller apparently claimed this was a courier mixup, changing her story from - her children were sick, then she was sick etc. I prefer Ping as it usually keeps me out of the weeds with seller (and buyers) but unfortunately, not this time as I copped some very aggressive emails from the seller when I queried delivery time frame. Eventually my trust in Ping was warranted.