@Poppy298
If you're in England, you don't need to send a formal cease and desist letter. You can immediately apply on a without notice basis for a non-molestation order.
If the court granted the order (which I think it would based on how he has treated you and the ongoing abuse), the order would need to be served on your ex, along with the evidence which you submitted in support of your application.
There would then be a further hearing (usually about 2-3 weeks later) at which he would have the chance to argue against the order remaining in place. Non-molestation orders are usually granted for a period of 6-12 months.
If you contact www.ncdv.org.uk/, they can talk you through the process. Our firm helps NCDV clients on a pro bono basis by helping them draft their witness evidence and the other paperwork. I've worked on about 25 applications. IME, even when the other party has challenged the non-mol, the court has upheld it. You don't need physical violence to justify a non-mol and many of the NCDV clients I have helped have experienced emotional and psychological abuse, not physical abuse.
Before you do apply for a non-mol, though, if the abuse is continuing, you may just want to convey the message to him - perhaps via your sister or a male third party - that if he continues with his abuse, you will go to the police. That may be enough to get him to back off and then you won't need to go through the bother of applying for a non-mol.
If not, you can then apply for a non-mol or indeed involve the police if his abuse seems to be escalating. If the police have a word with him, that might be enough to get him to stop.
Be vigilant, however, and for the time being, try to avoid being alone or in any situation where your ex might find you. Deep down, he hates women and he sounds capable of doing something nasty.