I was recently let go from WFB for "call-avoidance". I am terminally ill with a type of cancer and missed many days but my performance metrics were above listed performance requirements. I was taken into the office and made to listen to a call from six weeks prior, on a day that my phone was not functioning well (documented in company system) and told that it took me 12 seconds to answer my customer. I did service the call and even successfully referred a product but was let go because of the 12 second lag due to the system failure. If it were for missing work due to surgeries, I could understand but I feel that this was definitely a wrongful termination. They also never asked nor presented any documentation for me to sign or take home regarding the termination.

How does one proceed from here?

You can contact a labor attorney to see if you were wrongfully terminated but in most cases employees are "at will" employees and can be terminated at any time for no reason at all. Where do you live and what is WFB

Yes, it can depend on what country this is, and if in the US, what state.

It does look like they were looking for something to fire you for, They most likely did not want to do it for missing, because of your illness but wanted to fire you. They are not required to give you any warnings or paper work, unless that is required by their own company policy.
And in most cases, they may fire you for any reason, or even no reason. Just not for those reasons protected under law.