Your number is on a list of real numbers with real identities associated with them that was sold to them. Data brokers sell this information daily. They already know your number is real, but in order to comply with the law, they have to provide you with a legitimate option to opt out, so you will actually stop receiving correspondence from them if you ask them to stop (it is legally required). If not, they could be subject to a fine, but you’d obviously have to file a complaint with the relevant regulatory body for that.

If you don’t reply to opt out, they will continue sending messages to you in the future. It costs them almost nothing to do, so even if they didn’t know your number was real, they would do it anyway. Most of the people who donate from these messages don’t reply through text message anyway.

Political Communications to land lines are generally exempt from do not call. Cellular communications require prior consent, but the “consent” could be as flimsy as being registered with a certain party. You must be able to opt-out from the communication, and that’s why they have the “reply stop” verbiage. If they don’t honor your request, you should report it. Failing to actually make an effort to stop the communication (as is strangely being suggested) should be the only reason you would continue to receive them.

The direct affiliation with a party or campaign is not a requirement.

Here is the relevant information from the FCC fcc.gov/rules-political-campaign-calls-and-texts