How to shake an ex boyfriend

Me and my ex have been broken up for about 2 months after an 8 year relationship. After we broke up, he keeps texting and calling me nonstop. I've told him that I've found somebody and ever since then he's been hitting me up constantly. He's sending me threatening texts and he won't leave me alone! I'm getting sick of it now ! I just want him to stop and for him to move on a get on with his life ! Any advice on how to shake an ex?