The 31-year-old singer said she also sent a shocking foul-mouthed text to the music mogul, reported Daily Mirror.
"I can talk about this because I'm OK about it now. But I went through hell and it literally drove me mad. I became so desensitised, you could say terrible things to me and I wouldn't even think about it.
"I'd read awful stuff about myself and not blink. I shut down because I didn't know what else to do. Now I can say that Simon was right to get rid of me. I wasn't well in the head when that was going on, so it wasn't going to work. But he wasn't right not to tell me to my face," she said.
"I thought I had every box ticked, career and personal. I was the first to get married. I was the one everyone thought would be the first to have a baby and then the rug got pulled out from under me. I've learned that there is no such thing as a plan. You can't make them," she said.