You can block numbers for sure. I blocked a solisitor who was calling me 27 times a day, despite me telling them to stop. For my service provider it's easy, you log into the web site and add the number to a blocked list. I've never heard from them again.

I think the #1 thing trolls get off on is attention. So if you block his number and stop responding hopefully it fizzles out. But, if the texts are violent, maybe you should tell the police. Usually they don't do much about stalking, but if he's threatening you at all via text, you have proof.