Right i deal with this everyday at work.
Call your local police find their number on the internet. Explain the situation and request to see an officer about it. If they are anything like Lancs police they will book you a scheduled appointment to take a statement of complaint with a bobby. then let the police do the rest. they will go away and speak to the other party and words of advice given.
Generally what will happen is they will be warned off first. If they continue what they are doing they will be issued with a harrasement warning. If they still carry on they will be nicked and charged with public order charge and bail conditions placed on them not to contact you by themself or via a third party and to generally stay away. Technically he can be charged with harrasment if he has contacted you more than once as there is then a course of conduct, but this wont happen. But you've got to remember it takes a long time for things to happen, statements have to be taken packages put together, he has to be found, and if he doesnt want to be found that can make things drag on even longer. It can take a really long time to get to the stage where he is formally charged, but generally a warning is issued to them fairly quickly.
So you can contact the police and they will do something about, but dont expect the other person to just listen to them. If he's a dick which by the sound of it he is then he probably wont listen anyway and he will eventually get himself into trouble.
So the choice is yours really If youre going to contact the police best bit of advice is to keep any texy messages sent or messages on face or anything like that you can show to the bobby that comes round. But best of all dont play his games otherwise it will be seen as a tit for tat argument and very little will get done you will both be treated the same and you yourself could end up in trouble.