A-z claims going against us even with valid tracking

Recently we’ve had around 4-5 A-z claims go against us even though the tracking we’ve provided at the moment of dispatch shows that it was delivered. To make it worse, when we appeal and send over the exact time/date it was delivered and even pictures of the items in the customers hands the appeal gets turned down. So far we’ve lost around £700 worth of stock and easily £1500 of invalid refunds. Dies anyone else have this issue where amazon just ignores the evidence and refunds customers and does anyone else know how to stop this happening?