Ignore and don't ever reply - it could be anyone - a punter, a non punter, a woman hater, a wife/girlfriend, a troll another wg - anyone who is bored and has nothing better else to do.
Hope they go away. If it persists and you feel threatened, your only option is the police.
I have had similar e mails in the past, and ignore and block immediately.
Hope you are ok and you don't get anymore.
The last resort would be to get another phone number, but then they have won and has inconvenienced you - that is what they want.
Why can't people just be nice - it is not difficult? !!! x