How can I get help or file a complaint?

I cancelled by service with Xfinity - and have a credit.  They mailed it to the WRONG address and now asking me to wait an additional 45 days to refile my refund.  Since they mailed it to the wrong address, why can't they just credit me back on my credit card (which is how I paid my bills)?  I need a resolution as 1) customer services just kept transfering me, 2) no one had the foresight to CANCEL the existing check since it went to the wrong address 3) no one  seems to be able to CREDIT back my refund?  Who can I speak to directly who can help