15-20 a day? Wow, that's insane. I definitely do not have these problems, but then again I do some things to mitigate it, too.
I never put my real phone number in an online form when ordering something. If there's a problem with the order, an email will be just fine.
I also never put my real phone number down on a grocery store savings card application. These folks are the worst for selling your phone/emails.
I never link my real phone number to any social media.
I never give my real number as a recovery number to Paypal, Gmail or others.
Basically, I don't put my number down online or in a form anywhere. Folks like to sell that info.
All that said, occasionally something slips through and I'll get a call or two. A quick call to the Do Not Call registry fixes that right up. Don't know why others have so much trouble with the DNC not working.
These things are really easy to do and I bet I've had five spam calls in the last six months.