Use fakes. In the US there's a famous song called Jenny with the phone number 867-5309 in the lyrics. Everyone over age 30 knows that number by heart, and a fair number younger too.

Simply give (your local area-code)-867-5309 and there's a very good chance that someone's already signed up with that number. If not, I'll complete the signup with that number and whatever bogus name comes to mind. Jacob Blues, 1060 W Addison 60613 works well.

Just like AdNauseam, simply chaff the system until it's futile.

I'm sure there are similar characters in the public consciousness of every country.