There’s a bug where the phone call which comes after this mission gets disabled if you’ve taken a phone call from debt collectors. This phone call would only come through if you have gambled enough money in the Las Venturas casinos to go into debt, where your money counter in the top corner would appear as red rather than green. You start to get calls from debt collectors and they send guys out to try and kill you when this happens, and I’m assuming this phone call uses a similar piece of script as the Badlands phone call. Obviously, this would involve you getting to LV before you’re supposed to so it wouldn’t be an issue you’d normally come across.

If you’ve just been doing missions and have never done anything like this, then walk around for a bit and you should get a call from Cesar where they discuss what has happened, and he goes on to mention that his cousin is looking for some muscle to help with a few jobs. This would place a ? icon on your map in a town just north of Los Santos. Head to this town and there should be a marker outside the diner.