Hello laslow160,
Thanks for using the Apple Support Communities. We understand that you're attempting to setup an old pair of AirPods with a new charging case. It sounds as though you're using the actions from article, Set up your replacement AirPods or charging case. Is that right? Did you also follow the last steps mentioned by the * at the bottom of the page?
Is it possible that your old AirPods are actually first generation? If you have your old charging case, you can retrieve the serial number to verify. You can also compare the AirPods to what's shown here: Identify your AirPods.
Once you've identified they are both the same generation, and you're still unable to pair them correctly, reaching out to Apple Support at Get Support, would be the best option.
Best regards.