Why Seller Support So Bad

They only give you tension not get resolved or give proper reply. I sold a pc and amzon took 13 as shipping from buyer but the actual cost of shipping is 110 from every carrier i check and every platforms like pirateshipping, PayPal shipping. Now its been 3days i didn’t ship and support is not giving an solution. Buyer is not responding either for the email i send to ask “Due to shipping problems with amzon i cant ship, can i cancal if it is not resolved”. What you think?