Blacklisted

Its not my actual email that is blacklisted. I go to a group that I have been members with since 2006. Have always used Thunderbird with a gmail account, now for some reason I am getting the message that my IP has been blocked on account my IP is on a blacklist. What the heck?  I have tried to get access to posting anything on this group and am unable too. Been on the phone with Xfinity for the last 3 days and am not getting any help there keep getting the runaround  and hung up on, last night I know i spoke to at least  5 different people and its still not fixed. Xfinity you always want your customer to say good things about your business but honestly that is getting very hard to do dont know how you can say anything good about a company that does not even want to help their customers. Also if you cannot proved me with the services I pay for why should I give a good review and am seriously thinking about taking my business elsewhere.

Verna