Hello roisin259,
Thanks for using Apple Support Communities! We understand you have questions about the warranty for your AirPods case; let's look into this more.
The warranty that comes with your AirPods covers you against manufacturing defects, it does not cover accidental damage or loss:
Apple One (1) Year Limited Warranty – Accessory - For Apple and Beats Branded Products Only.
If you purchased an extended warranty through Argos, you would need to check with them directly on what their warranty covers.
You can see more about the cost to replace the case for your AirPods here:
AirPods Repair - Official Apple Support
Hope this helps.
Best Regards.