I sent an item using simple delivery and assumed all was well. I normally check tracking for items but as I'd sold a lot (moving house) in that week, I didn't realise this hadn't been delivered.  35 days after the due delivery date the buyer contacted me to say that Evri have not delivered the parcel and "please send a replacement"  (I can't; it was a 'one-off' item and I'm a private seller).  Having checked the tracking it states: "Parcel too damaged in transit to deliver; please contact the seller"
The item was double-boxed and not breakable so actually would probably be still okay to deliver (but after a month has probably been destroyed by Evri - or whatever they do when a parcel is considered too damaged to deliver). 
I have contacted the buyer twice asking her to open a case for non-delivery  (as both she and I should be protected by simple delivery and buyer protection fee). After a week, she still has not responded. Do I need to do more? I'm guessing she has missed the 30-day window to open a case which may be why I haven't heard back.