Internet personal data & big business -how do they get my info?

I went to change my password on ebay. I have never given ebay my past two or 3 phone numbers, have never given facebook my exact address or phone number

ebay has my phone number (willing to send me a text to verify) although they have been asking for my phone number for over a year via their generic operating software (I notice they don't ask anymore)

I had to give my phone number out after i moved for establishing some bills and now ebay has my number?

people say don't share your personal information but what is the point? I had to give companies my number to establish utilities and now a company i did NOT want to have my info does?? WTF!?!

i need education on privacy because my 1990's training is clearly outdated

i would much rather be close to 'off the grid' than a commercial statistic for big business and gov

i shouldn't ***** though because the chinese have ALLLLLLLLLLL of my most personal info and life history and social security number because OPM which runs the gov clearance got sloppy and hacked -even life lock doesn't help outside the U.S.

this constantly pisses me off what can we do?