Still billed by xfinity mobile after I've cancelled my services.

I canceled both my mobile and internet services early, and confirmed that my mobile service was immediately stopped on that day. Despite this, I was charged $42.12 for mobile in November on my credit card.

This is extremely frustrating — I had no active service after the cancellation date, yet I was still billed. I can not find direct message option. I want to know how to find a live agent to solve my problem!