Most likely, you did not generate or apply for your renewal certificate. Think of SSL like a passport – when the old one expires you must toss it out and apply for a new one. You should be able to see in your account or via an email how to generate or apply for your new order. If you have generated, make sure that the new certificate was approved and installed in place of the old expiring certificate. If the new certificate is installed, then the issue is with the configuration. Common solutions to this problem are to restart your webserver (http server), also to uninstall/delete the incorrect/old certificate(s).