royal fail

i been selling some stuff on ebay to make some money just getting rid of old bits and pieces anyway i sold a pandora charm to this lady in essex and after 3 weeks she was getting worried because she hadnt recieved it i had posted it 1st class 4 days after she had paid anyway long story short paypal forced me to refund her and royal mail wont compensate even though i sent them prove of postage and where i bought the charm from and the ebay listing