I assume there is no way to block somebody from texting or calling you, or is there?
Type your make and model of phone into Google and if it's possible to block from it.
Most Samsung phones will let you block numbers as I had to do this a couple of years ago. I just had to go into settings and select call rejection/auto reject. Not sure if this applies to all makes of phones though.
Worth a try before you go calling your service provider.
Of course as Jon said, there is nothing to stop that person from using another phone to contact you :(