The patent is indeed expired (there's a website that will tell you that date, but I forget its URL), but they can still sue for infringement that took place before the expiration date.

If the total damages are small (as it appears), then you are probably costing them more than the suit is worth. So I'd expect them to offer to settle for a token amount, to avoid having an official loss on the record. But IANAL and this is not legal advice.