My personal information obtained from where?

I have been receiving scam phone calls from Dell technical support, like many other users have posted on here and on Youtube and in nearly every thread there is a response from Dell thanking us for bringing this to your attention and claiming that no personal information is given out. YET, they have my NAME, DATE OF PURCHASE and SERIAL NUMBER. If you are not giving it out and protecting our data, how are they getting this information? It seems that you have been aware of this since at least 2014 yet they are still getting people personal information about purchases from Dell. I did fill out this form.