The seat back cover should be able to un-glove to get at the insides - find an auto upholsterer, maybe a trip there to show you how to get into the seat back, or open up a seam, this allows you look into the problem and hopefully fix it and then a trip back to re-stitch if required.
Or look into Borescope for phones - less than £10 on ebay - you can have a look inside the seat and work out if its fixable