Recieving nasty text messages

Please help me locate the owner of the following mobile number 07890481011 because whoever this person is they heve been sending me text messages of a nasty,insulting,theatening and distressing manner.They have started using the number above which is different from the one they were using back in june.I have rang the number and it just tells me the person i have called is not available and to leave a message.I am taking diasepam to try to calm myself down and to get my blood pressure down which is sailing dangerously high.It is someone who knows me or my fiance because they say my name (correctly spelt) and discribes mike my fiance also.The police don't want to know they just said change my sim card but this is a new sim card anyway so why should i have to again.Please help me why there is someone who we think cares for us but is doing this to stop us being happy.I know its someone we know well because no-one else knows my number besides my family and mikes family.This is scaring me because they might come after my daughters as they have already said they were coming to my work place and they said were i work and then sais they were coming to my home and said were i lived.Please help me my mobile company said i have to contact orange but i can't find a number