For the unused SD labels here's what you need to do:

• If you selected 'Buyer pays’ when you created the listing, your buyer will automatically be refunded for any Simple Delivery label that isn’t used after 30 days

• If you selected ‘Seller pays’ and offered free postage on your listing, you'll need to fill out the Request a refund for Simple Delivery form for the label that wasn’t used. Make sure to send your request within 14 days of your item selling.  Also ensure you add the replacement tracking number of the service used, and it shows delivery.

It hasn't been a smooth transition to Simple Delivery that's for sure, and still many issues to correct!

There is currently an issue that Simple Delivery not offering Custom Postage to oversize items,  lightweight items and those under £10,  these are all exempt from Simple Delivery.

There is a workaround.

From the link below Go To Solution and follow  the advice in Rick's answer to list your item.

https://community.ebay.co.uk/t5/Seller-Central/how-do-you-list-anything-bigger-than-61cm/m-p/7882638...

@sound-central