Q: Calendar malfunction vs. iCloud

I am continuously receiving email notifications from Calendar App regarding scheduled events, which are hidden by a notice which says a connection cannot be made to my Comcast account. Comcast is not listed as an account in Calendar. I do receive Mail from Comcast as they are my ISP. I think this has to do with iCloud somehow. Please point me to anything which might enlighten me. When this happens I have to Force Quit Mail. Complicated!