Telemarketers phone calls:
Just enter your number on "Do not Call" database at https://www.donotcall.gov/default.aspx
I do not get any telemarketers calls.
If someone still calls once in a while...this is what I do:
First response--> Can you put my number on "Do Nor Call" list?
They always answer--> I sure can. Thank you.
:End of Call.

Write down the name of company who made the call and number from your Caller ID.

If they call you again, you can get compensated as they are breaking the "Do Not Call" law.

Works for me.

Pre-Approved credit cards:
I addressed that issue by following instruction on this website.
https://www.optoutprescreen.com/