Buyers can't return Prime items?

Over the past few weeks I have been getting many buyers emailing requesting to return items.

Returns are auto authorised on Amazon but some customers can’t return, they have stated the return option is greyed out or they are presented with a message stating ‘this item is not eligible for a return’ I sell IT equipment so this shouldn’t be happening. The orders are within policy and sometimes only a few days old.

How can create a return on Amazon for the customer who are having problems and send them the Royal Mail 48 tracked returns label Amazon generates ?