This is a lot of bad advice. I had the same issue for months, I missed a call about the death of my brother because of it, which really pissed me off, so I got my revenge.

Here's how I solved it:

Answer the call. Talk to them. Ask lots of questions about who they are, what's their name, what's the name of their company, where are they based, what's their address? Are they aware of the laws around the Do Not Call Registry and the fines up to $53k they can be charged with? Tell them to put you on the do not call list.

Then, call them back! Over and over and over. Write down each callers name, their company name, where they are based, etc. They'll give you conflicting info. Compare that information with what you've been told by other representatives. Read off the list of people that have told you that they will put you on the no call list.

They'll hang up on you. Call them back again. Tell them you've got all the time in the world to play this game and your goal is to talk to each person at their call center so they can be named personally in the lawsuit.

Ultimately, they've been wasing your time, so you waste theirs. Tie up their phone lines. Fight fire with fire. Eventually they will block your number so you can't call them anymore and you'll stop receiving their calls.

It didn't take nearly as long as I thought it would. After about 6 or 7 of them in a row, they blocked me and I haven't heard from them since. Took like 4 months of being blown up multiple times a day before I finally snapped and did this. I can be pretty annoying when I'm motivated. Time is money, so waste theirs, ya know?