Need help extending Seasonal Convenience Plan — online error

My Xfinity Seasonal Convenience Plan end date is today, and I’m unable to extend or change the end date online. I get this error: “We are unable to complete your request at this time. Please try again later or call us at 1-800-Xfinity.”

Xfinity Assistant is also not responding — it only briefly shows “thinking” and then gives no reply.

Could an Xfinity Support agent please help me extend/change the end date of my existing Seasonal Convenience Plan?