Does anyone else have issues with their OH's ex's? My OH has a child with his ex which I don't have…

Does anyone else have issues with their OH's ex's? My OH has a child with his ex which I don't have a problem with but she seems to be trying to make our lives miserable! They've been split up for 8 years and she's been married for 5! I don't understand why she's being like this?! We have my OH son the majority of the time as that is what was deemed by social services yet she claims his child tax and child benefit and is demanding my OH pays maintenance. She's also threatened me several times for petty stuff like calling her son 'babe' I don't know how much more of this I can deal with as its putting a strain on the relationship of me and my OH! She seems to be able to ruin any happiness in the day that we have because she always kicks off about something petty!