If you are using the app, use a browser instead to make changes to all your addresses here (UK link):
https://accountsettings.ebay.co.uk/uas/addresses
Delete any old addresses, and make sure your current address is set as your primary address -- that is the address that should appear by default at checkout.
If you are using a browser and having problems use another browser, preferably the latest version of a popular browser with default settings and no add-ons enabled.
