obsessive ex! stressing me out :(

so my partner has twin 9 year olds to a horrible horrible woman.

since meeting my partner she has made it her mission to harrass me and force herself into our life together.

When we first met I was a nursery manager, and she took it upon herself to ring social services on numerous occasions making up lies about me, it caused me so much stress that I actually quit my job.

she stalks my Facebook (even though we are not friends on there) ringing my boyfriend at every opportunity claiming that any photos I post or statuses I make are to "wind her up"

she rings my partner on a daily basis to ask pointless questions. we have been together for 19 months now and are expecting our first child, (my first child anyway) it's getting to me so badly that I'm feeling like I have no option but to leave. being so angry wound up and stressed cannot be good for this little miracle growing inside me can it? I just don't know what to do.... me and my partner feel trapped in her bubble of viciousness. The police just give her a telling off and she continues a few days later... I just do not know what to do.

anyone else been through anything similar?