If your items are less than £10 and under 100g you should be able to opt out of Simple Delivery during the listing/revising process. Click on "Switch to advanced options" at the bottom of the postage section, and again on the pop-up you'll get.
For the current one you could cancel the transaction (refund will be issued) and relist without SD for the buyer to buy again.
You can also opt out of Evri just to be sure, via My eBay > Account tab > Selling > Postage Preferences > Simple Delivery > Courier Options > Edit. Or here's a direct link:
https://www.ebay.co.uk/ship/prf