forced to give mobile number to be able to get my emails!

Why was I forced to give you my mobile number for "security"? If I didn't give you my number I couldn't get in to my emails. some of us like to keep our numbers private so they don't get sold. so far I have never had cold calls on my phone and have had the same number for 16 years, it will be interesting to see if I do now. I asked for my number to be removed by the live chat and was basically told it couldn't be as its for security. I have had this email account for years and if my number doesn't get removed I will be deleting my account and want  it in writing that you have not kept any of my details