The return label is always for 2kg you would need to contact eBay Customer Services to provide the correct on.
However, for change of mind you should have opened a straight return case not one for item not as described. Here you, not the seller pays for that return label.
I would advise to take the item to the Post Office and pay for over the counter postage, and then contact eBay Customer Serv ices with the new tracking number to enter into the case.
To Contact Customer Services it's a Live Chat, or you can select to speak and request a Call Back. Click on this link:
https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid
On the left sidebar you can see Have us Call you or Chat with Our Automated Assistant.
On weekdays lines open between 8 a.m. and 10 .m.
On weekends they open between 9 a.m. and 6 p.m.
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