How does Afriforum get my contact number????

I have a tablet which I use only with Data and Wi-Fi, and it's NOT used as a telephone at all, although it has a number.

So the only people who have access to its number are myself, my wife and my service provider MTN. How the heck does Afriforum call me on this number, then tell ne they got it from a referral, but cannot tell me who from.

So maybe Afriforum or MTN could assist with where they got my number from?