Always respond with "You have the wrong number". This is the only way to actually get removed from these lists. It will take a while, because most of the people reaching out to you have paid a data broker for a list, and they get refunds/discounts for bad data, so they will report it back up to the data broker who will remove it. But this takes a while, and that number has already been sold multiple times to various campaigns, and also, its probably on more than one broker's list, so it takes a while to get it removed from all the brokers.

But it has worked for me:

I gave 10$ to a candidate once, and started getting texts every year for four years from multitudes of like-minded campaigns. I just told them wrong number every time and eventually, now, I get no more political spam texts.