If your X is turning your children against you by saying bad things about you and telling them lies, you need to stay calm and think long term. I understand that this sounds impossible when your heart is breaking. Getting through the next year without damaging your relationship with your children is essential to your long term happiness, so let the current stuff go and think long.
Unfortunately there is little you can do to stop parental alienation. If one parent is determined to bad mouth the other, you can not control this and the children suffer the most. The claim of parental alienation is put to the Judges so often and with such outrage in each and every case that it is rarely believed nor dealt with by the courts.
First, know that your children love both of you. They are not divorcing their parents. Your children are intuitive and they can and do figure out what is going on without any help from their parents.
The parent who is doing the bad mouthing is risking loosing their children in the long run. Children feel incredible stress when they are put in the middle, this is a situation that they will not forget.
If your children ask why is mommy/daddy saying _________ (fill in the blank); the best thing that you can say is something along the lines of “mommy/daddy is having a hard time right now but just remember, that mommy/daddy loves you”. This will allow your children to talk to you without fear of reprisal and they will keep you in the loop of what is being said. Trust me, the other parent is not allowing them to speak freely.
My X used to tell my children that there was “no money for food” and then go to Starbucks and out to lunch with his friends.
My children were not fooled, nor will yours. Have faith and tell/text/email/write to them saying that you love them, even if they are not talking to you.