i DON'T WANT to connect to icloud!!! how can i turn off this message 4EVER?

i have imac using os x el capitan 10.11.6. ever since i brought it online to internet 2 mos ago i am CONSTANTLY being asked if i want to connect to icloud (I DON'T)? with my macbook pro i only got this message once & then it got the message (for that day or session) but this imac just doesn't get it!!! i'll be working on a spreadsheet and everything freezes because that *#@!%^&*!!! message is on again.

in addition, for the last 2 mos i've run out of my anytime internet usage data within the 1st week of the month. i've turned off all automatic updates i can find which i'll check next month, but fear this automatic icloud reminder has something to do with the problem.

how can i get rid of the imac's warped perception that i want to connect to icloud???