5 out of 7 parcels not delivered after 8 Days Royal Mail, advice needed

soolin

I think the non delivery ‘curse’ passed to me reading this thread ! Just had a message from a buyer telling me that I need to do ‘something’ as the item they bought last Wednesday hasn’t arrived and I need to find it and get RM to deliver it today if possible but if not then tomorrow otherwise they will report me. 

I responded politely asking if they minded waiting another day or so and then opening an INR case as it was only 2nd class and I actually sent it next day rather than 2 days after purchase as per my listing. I’ve now got another message basically saying eBay said they would get it last weekend so I obviously delayed it somewhere and I need to phone RM and find out where it is so I can arrange delivery . All this for a £5 large letter bit of nonsense and for an established buyer with over 300 feedback.