I sold an item with postage details listed. Buyer bought through new eBay way of busing postage. Packaged it up & it’s now requiring a different weight & package size. I could usually change that before posting, but it was bought using the older wrong postage. How can I change it to the new weight & size, especially as the buyer has bought the item. If I took it to the post office they’d refuse it I’m sure as it’s wrong. HELP