My ex has been increasingly texting and leaving voicemails with regards to my parenting as well as requests/demands for money beyond the child support I already pay.

I'm to the point that I think I need legal help to stop the unwanted texts/voicemails. Talking with her has proven useless. Ignoring them doubly so.

Is there legal action I can take to stop this?

Have you been saving and keeping a record of everything? If you have you could get a restraining order and with it comes specifics for contact regarding the child.