Why Xfinity keep charging me for $330 after I quitted my phone plan? I need my refunds and online chat assistant is USELESS

I already transferred out my mobile phone plan to another carrier since Nov last year, and Xfinity kept charing me untill now.

In total, I'm looking at a $330 extra charge after i transition out. The online chat has been useless. Can I get support from this forum? 

Besides, I tried to follow the guidance from @XfinityChristy mentioned in this post but I cannot find the  "New message" (pencil and paper) icon upon getting to https://forums.xfinity.com/direct-messaging